Leo Jones was the brother of Martha Jones.
Leo was born to Clive and Francine Jones in 1987. (TV: Smith and Jones) As a child, he loved to read Commando comics (PROSE: The Story of Martha) and used to steal the tennis ball when his elder sisters, Tish and Martha, were playing in the garden. (PROSE: Wishing Well)
Circa 1990, Leo was responsible for breaking Martha's arm after he accidentally pushed her too hard on a park swing. Although Martha was the one with the injury, Leo was the one who ended up crying about it. (PROSE: The Frozen Wastes) He and Tish once buried Martha up to her neck in sand at Cromer Beach. (PROSE: Forever Autumn)
By 2008, Leo and his girlfriend had a two-year-old daughter named Keisha. (PROSE: Martha Jones' MySpace blog) He did not ask for a twenty-first birthday party and told Martha that he would rather not have one than have Clive and Francine arguing. Annalise bought him a 75p soap. The party ended in a fight, after which Leo went after his father whilst Tish stayed with their mother. (TV: Smith and Jones)
Leo witnessed Richard Lazarus turn forty years younger and the havoc that Lazarus created when he mutated and began a feeding frenzy to power his rejuvenation, during which he was struck in the head with a table and suffered a concussion. He also met the Tenth Doctor, who he could tell his sister loved dearly. (TV: The Lazarus Experiment)
On the day Harold Saxon took office, Leo was in Brighton with his girlfriend and daughter. Harold Saxon had his parents and sister arrested, but Leo evaded capture after Martha warned him to hide with friends. (TV: The Sound of Drums) Following the The Year That Never Was, Leo was back with the rest of his family as the only one without memory of the Toclafane invasion and its aftermath. (TV: Last of the Time Lords)