7. Billy The Kid
20th Century FoxThe most famous gunslinger in the Wild West, the obvious link to the series here is Ethan Chandler. At this point, much of Ethan's past remains unknown, including why it was he sailed to London in the first place. We get an inkling at the end of the first season during its final episode from a couple of men sent to track him down. We can infer from that that he clearly did something considered outside of the law. What if he ran with Billy The Kid's gang? And then maybe Kid, having faked his own death (the recorded historical one) comes after him to either forcibly re-enlist him or get some sort of revenge for a perceived past slight against him. We want a dirtier rougher around the edges portrayal here, Billy should be Ethan's dark reflection. To accomplish that, we like Josh Brolin for the role. The grittiness he'd bring to the show would be tangible.