Lucas is the son of Andrea Barr and the grandson of Sheriff Jake Devins. After watching his father die, Lucas stops talking. It appears that he is in some way connected to the spirit of Peter Sweeney and he is able to give Sam and Dean clues through crayoned drawings. Only when the spirit is at rest does he start talking again. During the episode Lucas seemed to form a connection with Dean who shared the trauma of watching a parent die. It was also Dean who ended up saving Lucas from the spirit Peter Sweeney in Lake Manitoc. This little boy learns an invaluable lesson from Dean: "Zeppelin rules!".
In Inherit the Earth, Lucas appears in the flashback sequence.