Change the Name of a Hero to one of the following. This can be done from Barrack under View Soldiers, clicking a Soldier, then going to customize. It can also be done from the customize menu on the deploy screen. Note, using one of these heroes will disable achievements.

Effect	Code
Unlock Joe Kelly - Heavy	Joe Kelly
Unlock Ken Levine - Sniper	Ken Levine
Unlock Otto Zander - Assault	Otto Zander
Unlock Sid Meier- Support	Sid Meier
Unlock Chris Kluwe - Sniper	Chris Kluwe