Alternate timeline

An alternate timeline is a reality which is different from a parallel universe in that historical events have been altered by a time traveller or other temporal phenomena. These alterations can be prevented from having ever come to pass, although memories of them are usually retained.

Timeline	Negated By	Featured in
Barbara Wright marries Ptolemy I and becomes Queen of Alexandria	alternate Barbara	VD: The Book of Shadows
The Dark Matrix terrorises England	Seventh Doctor and Ace	PDA: Matrix
Adolf Hitler uses the Timewyrm's power to enable Nazi Germany to conquer Earth	Seventh Doctor and Ace	NA: Timewyrm: Exodus
Nancy Grover uses Grold technology to become a goddess	Third Doctor and Liz Shaw	MA: The Eye of the Giant
The Power Elite take over Earth	Third Doctor	VD: Prisoners of the Sun
Freedom fighters from the 22nd century assassinate Sir Reginald Styles	Third Doctor and Jo Grant	DW: Day of the Daleks
Theodore Cassells's experiments lead to a global war which devastates Earth	Third Doctor	TVA: A Stitch in Time
The Doctor dies on Dust and regenerates	Eighth Doctor by destroying Gallifrey (EDA: The Ancestor Cell)	EDA: Interference - Book One, Interference - Book Two
Sutekh is freed and devastates Earth	Fourth Doctor and Sarah Jane Smith	DW: Pyramids of Mars
Melanicus creates the Millennium Wars	Fifth Doctor, Sir Justin and Shayde	DWM: The Tides of Time
Silurian Earth	Destroyed, not negated, by Seventh Doctor	NA: Blood Heat
The Doctor doesn't leave Gallifrey, allowing many alien races to invade Earth	Seventh Doctor, Ace and Bernice Summerfield	DWM: Time & Time Again
Pete Tyler doesn't die and Reapers begin consuming humanity	Pete Tyler	DW: Father's Day
Donna's World	alternate Donna Noble	DW: Turn Left
Andrea Yates' World	alternate Andrea Yates	SJA: Whatever Happened to Sarah Jane?
The Trickster's Earth	Eddie and Barbara Smith	SJA: The Temptation of Sarah Jane Smith
The Year That Never Was	Tenth Doctor, Martha Jones and Captain Jack Harkness	DW: Last of the Time Lords
Ship erases Sarah Jane Smith, Luke Smith and Clyde Langer	Adam Lloyd	SJA: The Mad Woman in the Attic
Humans don't evolve and Earth is a Tractis colony known as Paratractis	Eighth Doctor, Sam Jones, Jo Grant	EDA: Genocide
The Doctor and his companions become exhibits in the Moroks' Space Museum	First Doctor, Ian Chesterton, Barbara Wright, Vicki	DW: The Space Museum
Humans evolve into Haemovores	Seventh Doctor and Ace	DW: The Curse of Fenric
Daleks undergo the Mutant Phase	Dalek Emperor	BFA: The Mutant Phase
The Knights of Velyshaa conquer Gallifrey	Fifth Doctor, Sixth Doctor, Seventh Doctor, the Temperon	BFA: The Sirens of Time
The Nazis win World War II after a piece of laser technology is left at Colditz Castle	Alternate Eighth Doctor and Elizabeth Klein (Inadvertantly)	BFA: Colditz
The Progenitor Daleks repopulate Skaro and exterminate humanity to extinction	Eleventh Doctor and Amy Pond	VG: City of the Daleks
Amy Pond's parents Augustus and Tabetha fall into the crack and are erased from reality, leaving Amy to be raised by her Aunt Sharon instead	Eleventh Doctor and Amy Pond	DW: The Big Bang