Robert is Bobby Pancakes' werewolf alter-ego. After intentionally contracting lycanthropy in A Valuable Addition to Our Team (1.11), Bobby transforms into a werewolf to attack Davin Tyrill in the next episode. However, it is a great strain on his willpower and he is not entirely capable of controlling the bestial impulses.
Between Season 1 and Season 2, Bobby works on mastering his werewolf side, and that struggle is key to his decision to leave Waterdeep for Barovia. He struggles with this on his own and starts to chain himself up and gorge on steaks whenever the full moon rises.
By the point he transforms in Some Kind of Jazz Werewolf (2.05) a fully-fleshed second personality has emerged: Robert, a sexy, bloodthirsty monster and a real cool cat.
Later, Bobby tries to convince Glitter Gleam that Robert is some kind of performance art.
It's not clear how this will play out in Season 4 as they are on a starship and from space, moons are full all the time.