Jansen works for Leviticus Cornwall and is his secretary.
Events of Red Dead Redemption 2
Jansen arrives on ship with Cornwall and his men. During Cornwall’s discussion with Agent Milton, Cornwall orders Jansen to send a telegram to his business partners. Jansen then leaves in order to do so, but is seen being followed by Micah. During the ensuing shootout after Cornwall is killed, Micah is seen fighting with Jansen and knocking him out.