Walon Vau is a Mandalorian who was hired by Jango Fett to train squads of Republic Commandos; one of the Cuy'val Dar. Like Kal Skirata, he had to leave his home and everyone he knew behind and never leave Kamino for the duration of the training.
We don't know a lot about Vau yet, except that he trained both Delta Squad and Atin's old squad. He's described by some as 'borderline sociopathic', he's obsessed with tech and tactics, and he was involved in a demolitions incident with Scorch that left the two of them without eyebrows for a short time.