Jockey

Called the "Humper", "Creeper", "Back Humper", "Little Guy", "Leaper", and "Leapin'-on-your-back bitch", The Jockey is a new form of Special Infected that appears in Left 4 Dead 2. Jockeys jump onto the Survivors and cling to their head and upper-back. From there, they can steer the Survivor while clawing them.[1] The Infection has caused the Jockey to mutate a large amount of muscle upon his upper back and neck, causing him to hop around in a spider monkey motion. His fingers and toes have also increased in length, adding to his baboon-like profile. His lips and the skin surrounding them have also deteriorated away, giving him a more skeletal look at the mouth area. He has pupils, like the Spitter. He wears a tattered white t-shirt and blue boxers. He has a gibbering, ape-like vocalization, and cackles hysterically whilst attached to a Survivor. According to Valve commentary, the mutations have caused Mania in the Jockey, causing the Jockey to laugh uncontrollably.[2] While human the Jockey may have had scoliosis or ankylosing spondylitis which could explain why he has a hunched back.



http://left4dead.wikia.com/wiki/Jockey