Lawrence is Uncle Grandpa's guardian lobster who came down from the stars to show Uncle Grandpa a hypothetical reality of what would happen to his friends if it weren't for him in an effort to help Uncle Grandpa realize how important he is. He is voiced by Mark Hamill.
Lawrence is literally just a giant red lobster who floats
Lawrence is helpful and informative, always willing to explain things to Uncle Grandpa if he doesn't understand.
Lawrence may presumably be deceased at the end of the episode. However, this could be a lobster who looked similar to Lawrence or just his mortal body (since he lives among the stars).