Change a Soldiers name to any of the following names to unlock a Hidden Hero. Enter the name as you would any other, and once done, the game will ask if you want to summon a hero. These heroes all bear the likeness of the people whose names they're from and have very high stats. Summoning a hero will DISABLE achievements.

Effect	Password
Summon Joe Kelly, Heavy soldier equipped with Titan Armor and plasma tier weapons.	Joe Kelly
Summon Ken Levine, Sniper soldier equipped with Archangel Armor and plasma tier weapons.	Ken Levine
Summon Otto Zander, Assault soldier equipped with a ghost suit and plasma tier weapons.	Otto Zander
Summon Sid Meier, Support soldier equipped with Psi Armor and plasma tier weapons, as well as knowing all psi abilities including Rift.	Sid Meier
Summon William Carter, Assault soldier equipped with a Ghost Suit and plasma tier weapons.	William Carter