The Master (The TV Movie)

In one incarnation, the Master had his consciousness inhabit a morphant or deathworm body. In this form, he then possessed a Human, Bruce.

Preparations
The Master had earlier prepared for his execution on the Dalek homeworld Skaro by transferring his consciousness to a new host. One account claims that he absorbed a deathworm (EDA: The Eight Doctors), another that he used a Skarosian life form called a morphant (DWM: The Fallen) Whichever method he used, his consciousness survived the death of his physical body and escaped both the casket in which the Doctor stored his ashes and escaped from the TARDIS and escaped into San Francisco in the last days of 1999. (DW: Doctor Who: The TV Movie)

Takeover of Bruce
Subsequently, the Doctor got hit in the crossfire of a shooting and got picked up by an ambulance. Hiding in a bag inside an ambulance, he laid and wait as Bruce drove the ambulance's driver drove the Doctor to hospital. After Bruce had gotten home, the Master jumped down Bruce's throat, killing him physically and making him into a living corpse.

The Master, posing as Bruce, attempted to keep an eye on the Doctor. He befriended Chang Lee, a young local who had found the TARDIS key, with the eye to winning him over to his side. With Chang Lee, he entered the Doctor's TARDIS and regaled Chang Lee with stories of the Doctor's supposed villainy. He planned to open the Eye of Harmony and cause mass destruction.

In the meantime, the Doctor regenerated into a new form. After a confronation in the Doctor's TARDIS, the Master fell into the Eye of Harmony located there. The Doctor claimed that he had been "eaten" by the TARDIS. (DW: Doctor Who: The TV Movie)

Behind the Scenes
Gordon Tipple played the Master's previous incarnation, who appears only in a cameo and does not speak. Though the script to Doctor Who: The TV Movie referred to the Master in this form as a "morphant", this name does not appear onscreen.