John Hasler is an English actor and voice-over artist who appeared as T-Shirt in the children's TV series T-Bag from 1985–92. Hasler was the only character to remain with the show for its entire television run, starting as a young boy and leaving as a teenager.

He has appeared in Renford Rejects and Casualty and provided voices and automated dialogue replacement (ADR) for a number of TV, radio and film productions.

From 2015 onwards, he is the voice of Thomas the Tank Engine in the UK and Rheneas in the UK and US narrations of Thomas & Friends. He also voices the lead character on Teenage Fairytale Dropouts (as Trafalgar)