Flight Lieutenant Jeff Moreau aka Joker and the one screenshot I bet everyone has of him who has played the game. Well a lot of you anyway!
Joker is voiced by and to some degree modeled after Seth Green, the cutest Buffy werewolf in the history of the furry critters and the character is by far one of the biggest stars of the ensemble as well as the behind the scenes glue that holds the Normandy and its disparate crew(s) together with his quips and off-color remarks.
Seth has done a huge amount of voice work including but not limited to Robot Chicken, Avengers Assemble, Family Guy, Aqua Teen Hunger Force and Star Wars: The Clone Wars.
And I bet you didn’t know he voiced Howard the Duck in the after credits scene of Guardians of the Galaxy.
He’s also starred in several movies and appeared in several TV shows. You might be able to spot him as an expo fan in Ironman 2.