Resurrection of the Master

Many accounts held that The Master eventually died, only to be ressurected by a group of Time Lords, to fight in the Last Great Time War.

History
In one account of the end of the Last Great Time War, the TARDIS had long "suffer[ed]" since the High Council's resurrection of the Master before it eventually took a new shape following the fall of Gallifrey. (PROSE: Doctor Who and the Time War) Earlier, the Bruce Master had fallen into the Eye of Harmony within the TARDIS, which caused what the Eighth Doctor described as "indigestion" within the craft. (TV: Doctor Who)

By another account, the Master's resurrection was carried out by his own past and future selves following his death at the hands of the Ravenous. The other Masters had made a deal with the Celestial Intervention Agency to accomplish this, in return for them handing over Artron's technology. By this account, the Bruce Master had escaped the TARDIS before losing his human body, reverting to the Decayed Master who fell to the Ravenous. (AUDIO: Day of the Master)

Legacy
The Saxon Master, whilst speaking with the Tenth Doctor, recalled that the Time Lords had only resurrected him because they knew that he would be the perfect warrior for a time war. (TV: The Sound of Drums)