Orphan X (Orphan X #1) by Gregg Hurwitz

The Nowhere Man is a legendary figure spoken about only in whispers. It's said that when he's reached by the truly desperate and deserving, the Nowhere Man can and will do anything to protect and save them.

But he's no legend.

Evan Smoak is a man with skills, resources, and a personal mission to help those with nowhere else to turn. He's also a man with a dangerous past.

Chosen as a child, he was raised and trained as part of the off-the-books black box Orphan program, designed to create the perfect deniable intelligence assets—i.e. assassins.

He was Orphan X.

Evan broke with the program, using everything he learned to disappear.