He has the personality of a troublemaker, and has apparently been a constant source of torment for Ron at family functions. (Ron still remembers the time Shaun poured gravy down his pants.) He owns a pet iguana who apparently has made numerous attempts to eat Rufus. Unfortunately, since Shaun is still a little kid, Ron's complaints because of his behavior have been pretty much ignored.
Ron was unable to ditch him until Kim agreed to be Ron's date at his cousin Reuben's wedding, thus sparing Ron from having to sit at "the kid's table" (in Ron's words). Ron also resorted to using the Attitudinator device to make Shaun less annoying.
Shaun's last name is never given.
When Kim asked how old Shaun was, Ron supplied, "Seven, but he's an evil seven."
Shaun has only appeared in "Bad Boy".