Whopper

The Whopper is a bloated C-Virus infected Zombie which has expanded outwardly in size due to a build-up of gases that have generated due to the breakdown of enzymes in the body of the infected. It's also likely that in seemingly random cases the body responds to an infection by placing the body into an unchecked 'fat storage mode' which causes fat cells to be created at an alarming rate. Their thickened skin is also covered in lumps, fatty deposits and tumours.

The size and weight of a Whopper exceeds the normal limits of the human skeleton so it's also likely that the bones have increased in density due to the mutation. Although not confirmed nor documented it is assumed that the smell was revolting, even when compared to a normal Zombie.

In terms of durability, their large frame means that their internal organs are more heavily protected than a normal Zombie so they do take a lot more firepower to take down. Interestingly there was also a unique Whopper which was far larger than the common variants named the Supreme Whopper. It also wore a stretched t-shirt unlike all the others previously encountered which were shirtless.

The best way to deal with a Whopper is to aim for it's legs or it's ankles, as anything to get it onto the ground would give you a huge tactical advantage as it takes a great amount of energy for them to hoist their large frame back ono two feet - essentially taking out their legs makes them incapacitated.

It's likely that the Whopper was at least partially inspired by the Boomer from the Left 4 Dead series (although the Whopper does not explode). It could also be a tongue-in-cheek reference to the famous Burger King hamburger, a well-known high-calorie and fattening food.