Colin revealed that he and his family have just moved to Springfield from Ireland and that his father is a musician and humanitarian, but strenuously denies it's Bono from U2. Aside from that particular mention, none of the rest of his family is seen nor mentioned.
Colin and Lisa first met coincidentally whilst trying to inform Springfield citizens, in a door-to-door manner, of the pollution in Lake Springfield. They overhear one another and soon begin to finish each other's sentences on pollution. Lisa calls him dreamy whilst speaking to the town about the pollution in Lake Springfield, which greatly annoys neighbors.
During Trappuccino, due to an ensuing mob that comes after the Simpsons, Lisa was forced to leave Colin behind. As a goodbye Colin wrote a song entitled 'Lisa's Song' which he performs with his guitar, but unfortunately she cannot hear due to the Dome's thick glass wall. He then writes out the notes in marker on the glass so Lisa can understand the tune, which she does. After making sure Bart doesn't ruin the moment by punching him, she reluctantly leaves. Once Lisa returns to Springfield at the end of the movie, Milhouse claimed that Colin died, making a poor mimic of his voice to try to get Lisa to hold his hand due to his own feelings for her. He then appeared to Lisa's delight and they walked off together to get some ice-cream whilst holding hands. Lisa hasn't mentioned him ever since, leading to the possibility that the two of them broke up sometime between the movie and He Loves to Fly and He D'ohs. He has made one reappearance, being seen as a member of the rec center's art class.