Thomas Milligan

Thomas Milligan was a doctor who worked for the NHS in 2008. When the Master brought the Toclafane to Earth he became a fugitive. In 2009 during the Year That Never Was, he met Martha Jones when she returned to England and took her to see Professor Alison Docherty. When the Master tracked them down, he used his laser screwdriver to kill Thomas.

When the Master's paradox machine was destroyed, undoing the Year That Never Was, and reversing time back to 2008, Martha phoned doctor Thomas Milligan, and then hung up, reassured that in this timeline he was alive. (DW: Last of the Time Lords)

When Martha, now working for UNIT, joined Torchwood 3 temporarily as a medical officer, she mentioned to the flirtatious Owen that she had a serious boyfriend and that he had once saved her life. (TW: Reset) In fact, her online correspondence confirmed that she had initiated a relationship with Thomas Milligan. (WEB: torchwood.org.uk)

Martha later got engaged to Tom who was now a pediatrician working in Africa. (DW: The Sontaran Stratagem), Martha, however, married Mickey Smith instead of Tom (DW: The End of Time)

Peronality
Tom Milligan quickly took a liking to Martha Jones and proved to be very loyal to her, even trying to attack the Master in an attempt to protect her, resulting in what would have been his death if time had not been reversed so that the Master's reign had never happened. Although, from Tom's point of veiw, he had never met Martha, due to the fact that the "Year That Never Was" was erased from history, he later entered a romantic relationship with her. They were also engaged at one point but in the end Martha married Mickey Smith instead.

Though he was a doctor, Tom would not hesitate to deal with matters through force and kept a gun with him during the "Year That Never Was". He killed one of the Toclafane after it said that killing humans was fun and suggested using his gun to kill the Master but Martha explained that Time Lords couldn't be killed so easily.