Lock is a small trick-or-treating boy dressed in a red suit with red, pointy shoes, and a red mask to accompany the costume, making him look like a devil. The tail seems to be real as its found moving on its own throughout the movie. His skin is alabaster white while his hair and eyebrows are ruby red, fitting his devil costume.
He is the middle child of the three, with an age of six and appears to be the leader of the group.
He is, alongside Shock and Barrel, Oogie Boogie's henchman, but doesn't seem to be loyal to him, since he's often found doing odd jobs for Jack, too. He often quarrels with the other two Trick-or-Treaters and doesn't like it when he's being insulted or disrespected.
He and his cohorts are given the task to travel to Christmas Town and kidnap "Sandy Claws". On their first try they mistakenly take the Easter Bunny instead, which angers Jack, and are told to take the frightened Holiday Spirit back to his own world. They succeed on the second attempt on bringing "Sandy Claws" to Jack.
When Jack tells them to make the Christmas Spirit feel comfortable, Lock decides he should be shown to Oogie Boogie.
Later on when everyone in Halloween Town believes Jack is dead, Lock and the others "find" Santa Claus in Oogie's lair and lead the Mayor to him.
- It is unknown how Lock and the gang met Oogie.
- It is possible that they could be siblings, as Lock and Shock have similar faces.