Ellis is the son of two Ultra Sapiens that escaped from the government and were instrumental in the destruction of [[Project: USA:char:40993]]. Ellis and his parents lived alone with little to no contact from the outside world. He lived a normal life except that on Saturdays he was hypnotized and taught how to fight with and without weapons as well as other survival skills so he grew up thinking there were only 6 days a week. While he grew up, Ellis was taught the real history of America, including the people who are really in charge of things, but he was told nothing about Ultra Sapiens or Project: USA. One morning his family was attacked by Hunter-Killers and his mother(some sort of living fusion bomb) blew herself up to protect Ellis and his father. When the Hunter-Killers didn't stop coming, Ellis' father tried to kill him so the Hunter-Killer's wouldn't be able to take him and use the Catalog that they had put inside him when he was born. The Hunter-Killers wanted the Catalog so they could find other Ultras easier so they killed Ellis' father before he could kill his son. They took him to their base and after explaining to him what was going on (much of this explanation was lies) they got him to join the team in hunting down other Ultras. Ellis doesn't like that most of the Ultras they find get killed, but some are brought in alive so he continues to work with them.
Ellis' main power is the ability to mimic the powers of other Ultra Sapiens around him. This comes from having the catalog written on his genes. His other ability is limited precognition. He does things (without knowing why) that help him in the immediate future and when he acts on instinct he is always right. This may be his actual Ultra Sapien power but it is overlooked since the power of the Catalog is more obvious.
The catalog is a list of every Ultra-Sapien along with their powers. It was originally on a computer but when Ellis' parents destroyed [[Project: USA:char:40993]] they took it and had all the information written into Ellis' DNA. It lets Ellis be able to track down any Ultra and use their abilities. This is why the Hunter-Killers need Ellis on their team, because with him, finding and killing other Ultras is a simple task. The Catalog won't work if Ellis dies so the Hunter-Killers can't just kill him and take it.