In Army of the Dead‘s Zeus is the Patient zero and Alpha Zombie. He is a monster from an unknown origin who was being transported by the army but escaped during an accident near Area 51. He was then able to contaminate more people and invaded with several other zombies nearby Las Vegas, turning it into his playground and raising an army. This type of zombie is smart and able to make decisions as King Daddy was in Land of the Dead.
The movie sets up a unique zombie hierarchy consisting of both typical Shamblers and the more intelligent Alphas. A bite from Zeus turns humans into Alphas, whereas a bite from another Alpha turns them into Shamblers. The alphas are much smarter, faster, and stronger than their shambler counterparts.