Bruce Gerhardt (PROSE: The Novel of the Film) was an ambulance EMT in San Francisco in 1999 whom the Master possessed and, in effect, killed. On 30 December, he helped transport the Seventh Doctor and Chang Lee to Walker General Hospital after the Doctor's gunshot injury. He also unknowingly took the Master home with him. (TV: Doctor Who, PROSE: The Novel of the Film)
That night, while Bruce lay in bed snoring (much to the annoyance of his wife, Miranda), (PROSE: The Novel of the Film) the Master possessed his body, presumably destroying Bruce's consciousness in the process. One of the Master-possessed Bruce's first actions was to kill Miranda, after which he set off in pursuit of the Doctor's TARDIS and the Eye of Harmony within it. After a shaky start, the Master soon mastered Bruce's body, which eventually began to decay. He also adopted Bruce's American accent.
Bruce's body was eventually sucked into the Eye of Harmony in the Doctor's TARDIS and, presumably, destroyed. (TV: Doctor Who, PROSE: The Novel of the Film) While exploring the Eighth Doctor's TARDIS, River Song believed she heard an American screaming from within the walls. (GAME: The Eternity Clock)
According to one account, as the Eye of Harmony tried to break him down into pure energy, the Master managed to ride the energy into a spare room, which the Doctor's TARDIS then ejected into the Time Vortex to protect the Doctor. The Master would remain stranded in the vortex in Bruce's body for so many years that he had lost count. As a result of inhabiting Bruce's body, the Master found that he now lacked the mental defenses he possessed prior, and so he was susceptible to Kaliopi Mileska's ability to read minds. (AUDIO: The Lifeboat and the Deathboat)