Trillian

Trillian is a name used for multiple topics in popular culture and technology. Notable uses include a fictional character in The Hitchhiker's Guide to the Galaxy and a cross‑platform instant messaging client.

In Douglas Adams's The Hitchhiker's Guide to the Galaxy, Trillian (full name Tricia McMillan) is a human woman from Earth who joins the crew of the starship Heart of Gold. She travels with Ford Prefect, Arthur Dent, Zaphod Beeblebrox, and Marvin the Paranoid Android. Across various media—novels, radio, television, and film—Trillian is depicted as intelligent and composed, often serving as a rational counterpoint within the group. The character is one of the series’ recurring figures and has been portrayed by different actors in adaptations.

Trillian is also the name of a cross‑platform instant messaging client developed by Cerulean Studios. First released in 2000, the software aggregates multiple chat networks into a single interface, initially supporting AIM, ICQ, MSN Messenger, Yahoo! Messenger, and IRC, with later additions such as Facebook Messenger and Google Talk. Features commonly highlighted include multi-network messaging, synchronized history across devices, file transfers, and optional encryption. Trillian has been offered in free and paid editions and has expanded to desktop and mobile platforms, along with business-oriented versions under the Trillian brand.