Liam is one of Lincoln's schoolmates, and they appear to be friends. He looks to be proficient playing basketball.
His first appearance was in "Overnight Success", as one of the kids Lincoln invited to his sleepover, after Lincoln had a falling out with Clyde. Since then, he has made other appearances in other episodes.
He was the only person whom Lincoln's advice about girls works for in "Lincoln Loud: Girl Guru".
Despite getting a girlfriend in "Lincoln Loud: Girl Guru", in "Dance, Dance Resolution" he is dateless. It is possible that his girlfriend broke up with him prior to "Dance, Dance Resolution", the series' continuity is not consistent, or the episodes were aired out of production order.