The details of Annie and Clarabel's lives before 1946 are unknown. In 1946, they were given to Thomas when he started working his own branch line. They have had several adventures, such as losing their guard and becoming runaways.
When Thomas is away, Percy, Toby, Duck, Emily or Stanley takes his place to pull them. Emily and Neville have both taken them not knowing they were Thomas' coaches.
Annie and Clarabel are respectful to all of the engines, but most of all Gordon and Thomas. They are Thomas' best friends and are quick to rebuke him when he gets troublesome.