Roadhog is countered by heroes who prevent his actions and block his hooks, like Mei and Zarya. Heavy damage dealers such as Reaper can melt his health points.
Ana, Mei, Reaper, Zarya, Zenyatta
Heroes who counter Roadhog
Reaper is one of the best damage dealers in the game at a close range. He destroys Roadhog and most tanks while also healing himself for a percentage of the damage dealt.
Roadhog can mitigate a portion of the damage with Take a Breather, which grants healing and a 50% damage reduction, but it isn’t enough to survive against him.
Generally, Reaper will defeat Roadhog in the great majority of the duels. Thanks to Roadhog’s huge body and hitbox, Reaper can easily shoot him while also avoiding his attacks. Chain Hook is the only tool that can change the fate of this fight, but it is very predictable and easy to negate using Wraith Form.
Mei counters Roadhog by stopping him from doing his job. Using the primary fire of Endothermic Blaster you can slow and freeze him, so he won’t be able to escape, hook your teammates, or heal himself.
She is really annoying because freezing someone creates panic and prevents any action. Even if it is easy to headshot him with her secondary fire, Mei can’t kill him reliably in a 1vs1 situation - she needs the help of a teammate to kill a frozen Roadhog.
Ice Wall is a great tool against Roadhog because it blocks his hooks: if used at the right time, you can even save the life of a teammate who has been already hooked! This ability partially counters also Whole Hog as it blocks some damage, but it is just a momentary protection as the ultimate will break the ice pillars in a few seconds.
Zarya decreases the effectiveness of Roadhog because she can save herself or a hooked teammate by using her barriers, and at the same time also gain free charge. Thanks to this utility, she is a hero you will love having in the team when facing Roadhog.
A high energy Zarya is also able to annihilate him with the massive damage output of Particle Cannon.
Zenyatta is usually outside the range of Chain Hook due to his ideal position during a team fight. He is usually placed behind his team, providing heals and extra long-range damage.
Thanks to Orb of Discord, you are able to increase the damage of all your teammates against a single target, so you can just utilize it on Roadhog and alert your friends to focus fire him. In most cases, the help of a single DPS should be sufficient because Zenyatta alone can inflict a solid amount of damage by headshooting Roadhog with a volley of Orb of Destruction.
Every Roadhog player hates Ana because Biotic Grenades totally nullifies Take a Breather and any healing effect provided by the supports for 4 seconds. In this amount of time he is extremely vulnerable, so Ana and his team can kill him quickly.
Sleep Dart is also very annoying because it excludes you from the team fight for 5.5 seconds and can also be used to cancel Whole Hog.
General strategies against Roadhog
Positioning. An expert Roadhog will punish your positioning mistakes by hooking you in the middle of his team, and scoring a kill in most cases. If you get hooked, try to learn from your own mistakes: study the area from where he hooked you and place yourself in a more suitable position during the next fight on that point.
Cooldowns. Roadhog is very cooldown dependant. Chain Hook is the most dangerous ability as it can pull you out of nowhere and change the fate of a team fight. Take a Breather is decisive in a 1vs1 situation because if well-timed will heal Roadhog and nullify all your damage; then he will have the upper hand while you are reloading. Always punish a Roadhog that misses his hooks or uses the heal at the wrong time!
Friendly shields. Staying behind a shield will totally nullify any hook attempt. If there is a Reinhardt or Orisa in the team, use the safe areas behind their shields.
Hook range and map elements. Chain Hook has a limited range, so with many heroes you can fight from a long range and avoid them completely. Likewise, there are many areas of the map that can be used to block his hooks and hide a portion of your body.
Run for your life. If you still got hooked, and your hero can’t face him 1vs1, try to escape as quickly as possible - do not forget that Roadhog has almost no mobility. Your team might help with heals, a barrier, or an ice wall.
Heroes countered by Roadhog
Some players might wonder why Bastion is listed among the heroes countered. In Sentry mode, he is able to inflict a massive amount of damage (even more than Reaper), but at the same time he has no mobility, so it is one of the easier targets to hook for Roadhog. You need the constant protection of the team via shields and Zarya’s barriers to avoid it.
Most low-HP heroes aren’t able to kill Roadhog fast enough: he will heal himself and eventually hook and kill you.
I have indicated several heroes in the “strong against” section, including not only DPS ones such as Genji and McCree, but also healers like Mercy and Lucio who can’t survive a hook combo.
It is very frustrating to play a mobile tank such as Winston, D.Va, or Wrecking Ball against Roadhog because he can just hook them whenever they engage a teammate or attempt to escape from a nasty fight. Scrap Gun inflicts lots of damage at a close range, and all these heroes have big silhouettes that are hard to miss.
Note that Defense Matrix doesn’t block Chain Hook.
All the images and hero icons: Blizzard