Chang Lee

Chang Lee was a young Chinese man living in San Francisco in 1999. Chang and his friends were fleeing from a rival gang when the TARDIS suddenly appeared and the Doctor emerged being caught in the crossfire between the two gangs and shot. Chang managed to get an ambulance for the Doctor and get him to a hospital, where he died and regenerated into his next incarnation.

Later Chang met and became enthralled by the Master, who convinced the young man that the Doctor was evil. Only too late did Chang learn the truth, just before the Master killed him. Fortunately the Doctor was able to reverse time and resurrect Chang and Grace Holloway, whom the Master had also killed. After the Master's defeat the Doctor bade Chang farewell, warning him that he shouldn't be in San Francisco next Christmas. (DW: Doctor Who)

Trivia

 * Some fans consider Chang Lee to be a companion of the Doctor, but he is actually one of few known companions of the Master.
 * Both Yee Jee Tso and John Novack (the ER doctor) appeared in the fifth season of Smallville as kryptonite-infected metahumans.