How to unlock the second character?

[Darkion]

I already finished the game and got the 'break all 36 cages in the game' achievement. why is the second character (the one right next to Shepard) still blacked out?

[Zucchero]

play the first level on co-op and he should be in the wagon cage, I've heard it may take some tries however because cages seems to cycle through depending on how many heroes you've already unlocked? I've read also that if you start the tutorial on new game in co-op it gets unlocked immediately. Give one of these a try I guess