Oliver Queen (UE-43)

"Come on, he's Superman. I've fought beside him. He's the best we have. Oliver would've said that. Hell, they all would have."

- John Diggle

Oliver Queen was a vigilante and a friend of John Diggle.

Vigilantism
At some point, Oliver Queen became a vigilante, becoming friends with and working alongside John Diggle and Superman. He eventually died of unknown causes.