Tricia Marie McMillan, also known as Trillian Astra, is a fictional character from Douglas Adams' series The Hitchhiker's Guide to the Galaxy. She is most commonly referred to simply as "Trillian", a modification of her birth name, which she adopted because it sounded more "space-like". According to the movie version, her middle name is Marie. Physically, she is described as "a slim, darkish humanoid, with long waves of black hair, a full mouth, an odd little knob of a nose and ridiculously brown eyes," looking "vaguely Arabic."

Ford Prefect is a fictional character in The Hitchhiker's Guide to the Galaxy by the British author Douglas Adams. His role as Arthur Dent's friend – and rescuer, when the Earth is unexpectedly demolished to make way for a hyperspace bypass at the start of the story – is often expository, as Ford is an experienced galactic hitchhiker and explains that he is actually an alien journalist, a field researcher for the titular Guide itself, and not an out-of-work actor from Guildford as he had hitherto claimed.