Eli Strange was created by Detective Comics writer Tony Daniel.
Eli Strange was actually born Elliot Montrose. His mother Julia died giving birth to him. According to his birth records, there was no mention of who his father was. Eli was put into a foster home and by the time he was four, it became apparent to his middle class family that he was a gifted prodigy. Eli graduated college at the age of ten and started working for the Pentagon at the age of seventeen. His work for the Pentagon mostly consisted of decoding sensitive foreign diplomat communication. Eli left the Pentagon after both of his supervisors had died from suspicious freak accidents. It is believed that Hugo Strange is Eli's father, although Hugo is the man that ran the tests, so it may be a lie to get the intelligent boy to work for him.
Major Story Arcs
Detective Comics: Faces of Death
Russian Roulette (Backstory)
Eli works with Catwoman to steal back some diamonds that stolen from her by a rival gang.
Detective Comics: Scare Tactics
Hugo Strange uses Eli to operate an operation to doss Gotham with Fear Gas stolen from Scarecrow. This is broken up by Batman, who thinks that Eli was really a small boy kidnapped by the Scarecrow, and was looking to rescue him before he goes down a dark path. Batman realizes, after turning Eli over to the GCPD, that Eli has already gone down that path and might be able to be saved.