Liam started life far into our future. He witnessed his mother's death and never met his father.
He went on to become a part of the Time Agency as well as fall in love with Katrina Mills with whom he had a daughter called Elizabeth. Upon discovering the Time Agency was corrupt, he joined the "Rising Five". The plan was to travel back in time to change history and stop the Time Agency from ever happening.
Events here become far more ambiguous, but some between Liam escaping the Agency and travelling back in time, he travelled with the Doctor, a Time-Lord from Gallifrey, who died in his final incarnation, making Liam the final companion.
Liam escaped to 2007 Earth, taking the "blue box" with him, where he spent a year fighting extraterrestrial crime with his two friends Ben Goodlad and Dan the Cyborg. The problem was, he was running from something - a combination of the corrupt Agency and the tortured and twisted Agent Mortis - and had therefore stored his memories in a fob-watch, meaning he knew nothing of his life at the Time Agency. He later met Danny Gould, who became a part of the team. Events escalated during the "Battle for the Blue Box", and Liam regain his memory, before escaping and falling from sight.
Once again, it is uncertain what happened, but Agent Liam eventually returned to aid Ben and Dan in defeating the Zakatrons. When Ben died, Liam found himself with a diminished team in dire need of rebuilding. It was at this point Dr Robin Turner and Agent Mortis joined the team.
Liam later encountered Katrina Mills who hard also returned, but in a deluded, twisted form. He was forced to kill her, as she was the key to the Zakatrons obtaining a "Sun Destoyer" (although it later transpired to be Dan the Cyborg that was the key).
Finally the time came when the team were forced into the shadows by Vision-X Industries; this was what Liam had come back in time for: to stop the Time Agency.
In order to stop this dystopian future, Agent Liam later flew a Zakatron ship into the giant Flower Alien God that was roaming throughout Dartchester and was presumed dead. Agent Mortis later revealed that his Vortex Manipulator picked up traces of a time jump, with Liam now travelling around throughout time and space, with Mortis now in charge of building up a new team of Time Agent's to "follow in [Liam's] footsteps" and defend the Earth. However, it is still unknown as to whether the attempt to stop the Time Agency's corrupt attributes was effective or not.
"I want to look into the eyes of whoever is responsible, and bring them to justice!"