Mark Twain is a very fun and extroverted person, caring deeply for his co-workers, often even asking them to hang out after work which they usually refuse. He often makes jokes and is generally very lighthearted and laid-back, it's rare to see the man serious but when it comes to his weapons he can be; on missions he actually focuses. He's quite prideful about his abilities even keeping track of his successes in his "success diary" though he can acknowledge when others best him. 