Tank (Left 4 Dead)

"Yikes! It's a Tank! It's powerful enough to destroy my village! What should I do? Run or shoot?... RUN OR SHOOT?! Well, why can't that thing be on our side?"

--Su Ji-Hoon, The Power of Wealth and Fear

The Tank is a Special Infected that is arguably the most powerful among the Infected in the game, along with the Witch. Unless the team works together to take the Tank down, it can wipe out the whole team single-handedly, or with the assistance of other Special Infected.

In When the Cold Breeze Blows Away, like Brutes, they are heavy, powerful infected zombies that serve for the Undead Alliance.

Extant of Mutations
The Tank is an exclusively male Special Infected who has experienced the most extensive physical mutations of any other class of Special Infected. The most obvious trait is his extreme hypertrophy, or abnormally increased muscle mass. Despite his enormous bulk, the Tank is incredibly fast and agile, able to keep up with even a healthy survivor.