Thinking of making a hitman for the team, if allowed. Though since I imagine actual assassination jobs would be fairly rare, he could double as a bodyguard or provide some valuable intel on the side. Most likely he'd glean information from his underworld contacts for a fee or in exchange for a favour (often a deadly kind).

He'd likely be in his 40s, so plenty of opportunities for past encounters with other characters. May or may not have a protégé under his wing.