The Zombie is one of the main enemies of the Reason 4 Life series who seemingly changes it appearances and stats in Reason 4 Life 3, and 4. Their ability is to swarm in hordes of at least 3 or higher. The other name you could call them is a Horde as that is their only ability whatsoever.
They are a little bit slower then the player but do good amounts of damage per touch or hit. They can kill one player in probably five seconds or else due to their amazing strength and ability to swarm. To make it much worse they can seemingly climb ladders, that surprised you right? It should, because they may be considered weak but unlike in Left 4 Dead they are very strong and can wipe out groups of survivors if in a large enough swarm.
The zombie is a human being or person, who has been infected with the contagious green flu.