Carter Bell

Carter Bell is one of the playable characters in Lara Croft and the Temple of Osiris. He accompanies Lara Croft, Horus, and Isis on their quest to destroy the evil god Set and his minions.

He is a rivalling Archeologist and treasure hunter who independently of Lara has been searching for the Staff of Osiris. When he is the first to find it, he accidentally sets free Set from the Underworld of Duat.

So for no further background story has been provided by Square Enix.