Lieutenant Commander Shepard is the human protagonist of Mass Effect, Mass Effect 2, and Mass Effect 3, whose gender, appearance, skills and pre-service history are all customizable and have an impact on the story. Shepard's first name is also customizable, but is never stated in-game. The default pre-made Shepard is a male Soldier named John, with the Earthborn/Sole Survivor profile.
Shepard was born on April 11, 2154, is a graduate of the Systems Alliance N7 special forces program (service no. 5923-AC-2826), and is initially assigned to the SSV Normandy as Executive Officer. Shepard later becomes the first human to join the Spectres, an elite special task force for the Citadel Council.

The male Shepard is voiced by Mark Meer, and the female Shepard is voiced by Jennifer Hale.

Trivia
Commander Shepard is named after Alan Bartlett Shepard, Jr., the second person and the first American in space (May 5, 1961). He later commanded the Apollo 14 mission in 1971 and became the fifth person to walk on the Moon.

Shepard's birthday (April 11) is the same day that Apollo 13 (an American attempted manned moon landing mission that almost ended in disaster) was launched (April 11, 1970).

In the advertising for Mass Effect and Mass Effect 2, only a male Commander Shepard was depicted. For Mass Effect 3, BioWare created a trailer featuring a female Commander Shepard for the first time. In addition, the boxart for the Xbox 360 version of Mass Effect 3 was made reversible; featuring a male Shepard on one side and a female Shepard on the other.

The default male face for Shepard is based on that of Dutch model Mark Vanderloo.

Shepard seems to speak with a hint of Canadian dialect. This may be because Mark Meer and Jennifer Hale, the voices of the male and female Shepard respectively, are Canadian.

The female Shepard is played by prolific voice actress Jennifer Hale, who voiced Bastila Shan in BioWare's Star Wars: Knights of the Old Republic. Hale also provides the voice for Satele Shan and the Female Republic Trooper in BioWare's MMO Star Wars: The Old Republic.

When Shepard is inducted as a Spectre, according to Admiral Hackett Shepard is, technically, still part of the Alliance military (though Captain Anderson claims otherwise). Therefore, Shepard should still be referred to as a Commander, even though Shepard is outside of the Alliance military's chain of command and answers directly to the Council.
Military ranks can, in some situations, be deferred in favor of civilian ranks. Considering the nature and authority of Spectres, it is likely that this is considered to supersede any military rank.

The default names of both the male and female Shepard are the names for an unidentified male (John Doe) and female (Jane Doe) respectively.