1)  Lucio:  Lucio's auras are very useful for Roadhog.  Lucio's heal aura can provide a slow consistent healing for Roadhog, allowing him to not use his Take a Breather as often and keeping the Scrap Gun blasts going.  Lucio's speed aura makes up for Roadhog's poor mobility, allowing him to avoid enemy ultimates, move in and out of combat quickly to Chain Hook enemies in, and to get back to the fight much faster after dying.  Speed aura also makes Roadhog's movement while using Whole Hog much faster, enabling him to position himself better while using it.  Keep in mind that Lucio's auras only work when you stay within 30 meters of each other and keep line of sight with him as well.

Lucio can protect Roadhog up close from deadly close range heroes such as Mei's freeze gun, McCree's Flashbangs and Reaper's shotguns by blowing them away from Roadhog with his Soundwave ability.  Roadhog can also protect Lucio from getting ambushed by using Whole Hog to knock enemies away from him or by Chain Hooking enemies away from Lucio.

Lucio's ultimate Sound Barrier provides Roadhog and his team with powerful temporary shields which allows Roadhog to have the opportunity to be more aggressive at moving in the front lines to Chain Hook enemies into him and getting clearer Scrap Gun shots in.  Sound Barrier also pairs well with Roadhog's Whole Hog, as normally Roadhog is vulnerable while using it and Sound Barrier can ensure his survival during it.

2)  Zenyatta:  Zenyatta's Harmony Orb can be a decent way to heal Roadhog up slowly, not nearly as effective as Mercy's healing beam, but it can enable Roadhog to be more aggressive at staying in the front lines to use Chain Hook and fire Scrap Gun shots out.  Although keeping Roadhog healed isn't a prime concern for Zenyatta due to Roadhog's Take a Breather (self-heal) and he is usually better off giving it to other allies that have poor mobility to reach health packs or means of self healing.  When Roadhog uses Whole Hog, he can greatly benefit from the Harmony Orb as he tends to be very vulnerable while using it.

When Roadhog Chain Hooks an enemy into him, Zenyatta can give that enemy the Discord Orb to ensure the death of the chained in victim, this becomes especially valuable against high HP tanks.

Be mindful of which enemy has received Zenyatta's Discord Orb as that should be a prime target for Scrap Gun shots.

Zenyatta is a very squishy support hero and he is very prone to getting flanked by offensive enemies.  Roadhog can protect Zenyatta by Chain Hooking flankers away from him and he can also use Whole Hog to knock enemies away from Zenyatta.

Zenyatta's ultimate Transcendence is a powerful team healing ability, which can enable Zenyatta's team to advance forward giving Roadhog easy opportunities to Chain Hook enemies and get closer to fire Scrap Gun shots off safely.

3)  Mercy:  Mercy's healing is by far the single best allied healing capability in Overwatch.  Roadhog can be a great target for Mercy to heal, especially if Roadhog is being attacked by multiple enemies at once.  Keep in mind that Mercy gains ultimate charge while healing enemies, so you should refrain from using Take a Breather if you know Mercy can just heal you instead.  Only use Take a Breather if Mercy is busy supporting another hero or if you are taking too much damage quickly.

Mercy's damage boost works great on Roadhog's Scrap Gun.  When Roadhog Chain Hooks an enemy into him, Mercy can switch to her damage boost to ensure the chained in victim dies from the Scrap Gun shot up close.

It can also be effective for Mercy to damage boost Roadhog's Whole Hog, but generally only if he is closer up to his enemies and the majority of the shrapnel rounds connect to his targets, otherwise damage boost is not so effective on Whole Hog.  Whole Hog's main use is to knock back enemies, not necessarily for damage.

Roadhog's extremely poor mobility makes it very hard for him to get back to the fight faster after dying, so he greatly benefits from Mercy's ultimate Resurrect to get back to the fight very fast.  Since Roadhog is one of the most self sufficient tanks, he can usually take care of himself after he gets resurrected, even if there aren't too many allies around him at the time.

4)  Ana:  Ana works great with Roadhog because of Ana's Biotic Grenade's use with Roadhog's self-heal (Take a Breather) ability.  When a Biotic Grenade is struck on Roadhog, it will make his Take a Breather ability fill 100% of his life up.

Roadhog's big hitbox makes it very easy for Ana to aim Biotic Rifle shots at him in case he needs some quick healing, even from long ranges.  Ana should keep an extra eye on Roadhog when he uses Whole Hog, as he is unable to use his self-heal during that time.  Ana's Biotic Rifle shots can keep Roadhog's ultimate going longer and more effectively.

If Ana misses a Sleep Dart on a close up flanker, Roadhog can potentially save Ana by Chain Hooking the victim into him.

Nano Boosting Roadhog (Ana's ultimate) is generally a good idea.  Nano Boost allows Roadhog to quickly move around to line up Chain Hook throws more efficiently. The increased damage reduction and damage output allows him to be much more aggressive at doing basically what ever he wants to do without too much worry, even while he is using his ultimate Whole Hog.

5)  Symmetra:  High hitpoint tanks like Roadhog doesn't benefit from Symmetra's Photon Shield as much as squishy heroes do, but the little extra shield can allow Roadhog to withstand some extra damage while he tries to Chain Hook his enemies and giving him some extra time before needing to use Take a Breather (self heal).

Symmetra can place her Sentry Turrets at a choke point enabling Roadhog to have easy slowed targets to use his Chain Hook on if enemies try to make an advancement.

Roadhog's big hotbox can act as a meat shield for Symmetra to get behind to safely fire her Photon Orbs, it's not as effective as Reinhardt's shield or Winston's barrier, but it can provide some protection.

Roadhog's extremely poor mobility makes it very hard for him to get back to the fight faster after dying, so he greatly benefits from using Symmetra's Teleporter to get back to the fight very fast.

Symmetra is almost hopeless when she is being attacked by multiple enemies up close, but Roadhog can use Whole Hog to knock enemies away from her or he can Chain Hook one of the enemies away from her.

1)  Reinhardt:  Reinhardt's shield works amazingly well with Roadhog.  Reinhardt's shield enables Roadhog to safely stay in the front lines to Chain Hook enemies, use Take a Breather and also use Whole Hog safely and more effectively.  Being able to push forward safely behind Reinhardt's shield while Chain Hooking enemies in is a powerful synergy between these two heroes.

After Chain Hooking an enemy in, Reinhardt can do a Rocket Hammer swing at the victim to ensure the victim will die.

Reinhardt's ultimate Earthshatter will drop down and stun enemies, giving Roadhog an easy target to Chain Hook.

Roadhog may not want to use Whole Hog against dropped enemies from Reinhardt's Earthshatter, as they will be knocked away, potentially giving your team a harder chance to counter the dropped enemies.

2)  Zarya:  Zarya's Projected Barriers are useful with Roadhog because he tends to go in the front lines often to Chain Hook enemies and he doesn't have personal shields like other tanks do.  Roadhog can also benefit from receiving a Projected Barrier right after he Chain Hooks an enemy into him, as any damage done back to Roadhog will just power up Zarya's weapon and protect Roadhog at the same time.

It's usually difficult for Roadhog to avoid enemy ultimates due to his poor mobility, but with Zarya's Projected Barrier he can get away from virtually every enemy ultimate in the game safely.

Roadhog can potentially save Zarya from deadly close up enemies such as Mei (and her freeze gun) or Reinhardt (and his Rocket Hammer) by Chain Hooking enemies away from her.

Roadhog's Whole Hog can be paired up with Zarya's ultimate Graviton Surge.  If you see her use Graviton Surge, Whole Hog can be effective against the clumped up enemies, but you would need to get somewhat close to the clumped up enemies to do enough damage which can be dangerous for Roadhog.  Obtaining a Projected Barrier would dramatically help your situation during this time, or some other protection.  The second best thing for Roadhog to do against enemies stuck in Graviton Surge is to just fire Scrap Gun shots at the clumped up enemies.

While anytime using Whole Hog, Roadhog is generally very vulnerable and he benefits from Zarya's Projected Barrier during this time.

3)  Winston:  Winston's Barrier Projector (shield globes) are very beneficial for Roadhog to take cover from and fire Scrap Gun shots along with throwing out Chain Hooks safely.  Winston also has the capability to Leap towards Roadhog when in need to quickly throw down a Barrier Projector for protection.  Barrier Projectors can also enable Roadhog to safely use his Take a Breather ability (as normally Roadhog is vulnerable while using it because he is stunlocked for a second).

Both Winston and Roadhog's ultimates have similar uses, they are both used to knock people away (but with not so much damage).  Besides providing double the knock back power, there isn't too many synergies between the two ultimates.  Although Winston can put down a Barrier Projector to protect Roadhog while using Whole Hog, which is very effective because Roadhog is normally vulnerable while using it.

4)  D.va:  D.va can knock enemies back with her Boosters, potentially giving Roadhog easier targets for Chain Hook.  D.va can protect Roadhog with her Defense Matrix ability, this can allow Roadhog to safely use Chain Hooks up close along with using Take a Breather more safely.  Defense Matrix can also protect Roadhog while using Whole Hog as well.

Both D.va and Roadhog's ultimates are made to clear enemies out of a path, as such there isn't much synergistic use between the two of them.

5)  Roadhog:  Two Roadhogs provide twice the Chain Hook power, but lacks flanking potential and damage mitigation (no shields).

Two Roadhog's using Whole Hog at the same time can provide an insane amount of knock back power, but it's usually overkill for both to use Whole Hog at the same time.

1)  Soldier 76:  Even though Roadhog has a self heal of 300 (half of his HP) every 8 seconds, Soldier 76's Biotic Fields are still very useful for Roadhog.  Biotic Fields can still keep Roadhog in the fight often, allowing him to refrain from using his self heal as much along with making it safer for him to Chain Hook enemies up close.  Roadhog is also usually right around Soldier 76 to take advantage of his Biotic Fields often.

Roadhog's Whole Hog can scatter enemies around giving Soldier 76 an easier time to pick off disoriented enemies from the knock backs of Whole Hog and can make it safer to use his ultimate Tactical Visor in this situation.

It's usually a good idea to make sure Soldier 76 puts down a Biotic Field under Roadhog while using Whole Hog, as you are vulnerable while using it because you cannot cancel the ability or use your self heal during your ultimate.

2)  Widowmaker:  Widowmaker's Infra-Sight allows Roadhog to prepare a Chain Hook before an enemy comes around a corner/wall.

Roadhog's Whole Hog can scatter enemies around giving Widowmaker an easier time to pick off disoriented enemies from the knock backs of Whole Hog.

3)  Torbjorn:  When Roadhog Chain Hooks an enemy into him it can expose the victim to Torbjorn turret, this can ensure the death of the chained in victim.  Every time a Roadhog Chain Hooks an enemy into him there is going to be a good chance that an easy to collect Scrap piece for Torbjorn can be collected from the death of the chained in victim.

Out of all the tanks I believe that Roadhog benefits the least from Torbjorn's Armor Packs due to his already large hitpoints of 600 and his self-heal of 300.  Even then, Armor Packs can still help him a little to soak up even more damage in the front lines and to delay the use of his self-heal for a later time.  Armor Packs are most useful on Roadhog while he is using Whole Hog as he is generally vulnerable while using it and he cannot use any other abilities (including his self-heal) until the ultimate is over.

4)  Mei:  Sometimes being up close trying to freeze enemies can be risky for Mei, but with Roadhog, he can Chain Hook one of the enemies so Mei has less enemies to deal with up close.

Keep in mind that Roadhog can also Chain Hook frozen enemies into him.  Frozen stationary enemies are easy Chain Hook targets for Roadhog and it can be useful for him to Chain Hook frozen enemies into him if he gets the chance.

Mei can assist Roadhog with Ice Walls to block enemies from going after him while he uses his Take a Breather self-heal ability or even with enemies chasing after him due to his slow mobility.

Roadhog's Whole Hog doesn't have much synergistic value with Mei, and Mei's Blizzard doesn't have much synergistic use with Roadhog as well.

5)  Hanzo:  Hanzo's Sonic Arrow allows Roadhog to prepare a Chain Hook before an enemy comes around a corner/wall.

Roadhog's Whole Hog can scatter enemies around giving Hanzo an easier time to pick off disoriented enemies from the knock backs of Whole Hog.  Whole Hog can also be paired decently with Hanzo's ultimate Dragonstrike as the knocked back enemies can have a harder time dodging the Dragonstrike.

6)  Pharah:  Roadhog's Whole Hog can scatter enemies around giving Pharah an easier time to pick off disoriented enemies from the knock backs of Whole Hog, and can also be an okay time for Pharah to use her ultimate Barrage as well.

Roadhog can Chain Hook and kill a lot of enemies that can give Pharah some problems, including Soldier 76, McCree, Hanzo, and D.va.

1)  Reaper:  Roadhog's Whole Hog can scatter enemies around giving Reaper an easier time to pick off disoriented enemies from the knock backs of Whole Hog.  Whole Hog can also make it safer for Reaper to use his ultimate Deathblossom.

If you see Reaper using Deathblossom, keep an eye out for any Genjis in the area as that should be a prime target for you to Chain Hook and eliminate first as Genji is a great counter to Reaper's Deathblossom with his Swift Strike and Deflect combo.  Other heroes to Chain Hook while Reaper is using Deathblossom includes:  an enemy Roadhog (a Chain Hook will stop it) and McCree (his Flashbangs will stop it).

2)  Junkrat:  Roadhog benefits from Junkrat's Steel Traps while he uses his self heal, as he cannot do anything else while healing himself.  The Steel Traps can keep enemies away from him during these times.

Whole Hog has neutral use when combined with Junkrat's ultimate Rip-Tire.  Even though the knocked back enemies will have a harder time shooting down a Rip-Tire, it can make the tire have less of an impact when it explodes potentially killing less enemies and also can make the tire have to travel further to reach the knock backed enemies.

Roadhog can protect Junkrat while he is using Rip-Tire by Chain Hooking enemies that are approaching his stationary character.  Roadhog can also get in front of a Rip-Tire to protect it from enemy fire.

Roadhog's Whole Hog can scatter enemies around giving Junkrat an easier time to pick off disoriented enemies with frag grenades.  Whole Hog can also allow Junkrat to do an aggressive mine jump while the enemies are getting knocked back, making it easier for Junkrat to reposition himself.

3)  McCree:  Roadhog's Whole Hog can scatter enemies around giving McCree an easier time to pick off disoriented enemies from the knock backs of Whole Hog.  Whole Hog can also be paired decently with McCree's ultimate Deadeye as the knocked back enemies will have a harder time aiming at McCree while he is revving up his Deadeye shots.

4)  Bastion:  With Roadhog's large hitbox, he can get in front of a Bastion Sentry to block shots from hitting him, but this can also make it harder for Bastion to aim at enemies since it will be harder to see what's in front of him.

Roadhog's Whole Hog can scatter enemies around giving Bastion an easier time to pick off disoriented enemies from the knock backs of Whole Hog and can make it safer for Bastion to use his ultimate Tank Form in this situation as well.

Chain Hooked enemies can allow Bastion to get some easy shots on the chained in victim.

5)  Tracer:  Roadhog's Whole Hog can scatter enemies around giving Tracer an easier time to harass the disoriented enemies from the knock backs of Whole Hog.

Tracer's harassing distractions can make it easier for Roadhog to Chain Hook enemies into him, which in turn will give Tracer an easier time to harass with less enemies to deal with.

6)  Genji:  Roadhog is an independent tank that doesn't have many synergies with Genji, although Roadhog's Whole Hog can scatter enemies around giving Genji an easier time to pick off disoriented enemies from the knock backs of Whole Hog.