Annie and Clarabel are faithful coaches that belong to Thomas. They help him carry passengers and luggage all around the Island of Sodor. Annie is a coach who only carries passengers. Clarabel is a called a composite coach because she has two compartments, one for passengers and the other for luggage.
Trivia
Annie and Clarabel have appeared since the very first season of the show. When Thomas is pulling his favorite coaches Annie and Clarabel, Annie is the first coach and travels facing him while Clarabel always travels in the rear facing away from Thomas.