There are many options that the player is able to choose concerning Commander Shepard's history and origins. Shepard can either be male or female; his birthplace can be earth, an off-world colony, or somewhere in space (ie. a ship or space station); and may have a sole survivor, war hero, or ruthless psychological trait. At the time of the first Mass Effect, Shepard was born on April 11th, 2154 and is approximately 29 years old. He enlisted in the Alliance at 18 years old (2172). Shepard's personality throughout the game is mostly determined by the choices the player makes in both dialogue and action.
The default male Shepard, the model used by BioWare for trailers, is called John while the female default name is Jane; both defaults are of the Soldier class.