First Doctor/Other realities

Alternate timelines
In an alternate timeline created by the Discordia, the Doctor had a passionate romantic relationship with River Song that began in his first incarnation, having married her by his fourth incarnation. The Doctor would have difficulty "smuggling" River into the Capitol through the Cloisters. (AUDIO: Someone I Once Knew)

In an alternate timeline created by the Black Guardian as revenge on the Doctor, the First Doctor never left Gallifrey, eventually becoming Lord President and forming an alliance with the Dalek Empire. The Seventh Doctor, Bernice Summerfield, and Ace, with instructions from the White Guardian, were able to retrieve the Key to Time to set the timeline straight. (COMIC: Time & Time Again)

When the Valeyard used his control of the Dark Matrix to corrupt the Doctors, the First Doctor's corruption occurred when he murdered other Time Lords in order to leave Gallifrey. This timeline was later undone by the Seventh Doctor. (PROSE: Matrix)

Averted timelines
When the TARDIS crashed on Tick-Tock World, the Doctor, along with Ian and Barbara, were devoured by the Xesto, creatures that consumed time and all possible futures. He then woke up in a dream-like dimension, encountering other alternative outcomes of how he could have been devoured. A woman helped him to make contact with Susan, as the state of "death" on the planet meant someone would be disposed outside time itself. As he was fading away, he realised the woman was an older version of his granddaughter, and he persuaded the younger Susan to touch her older self. Their violation of the Blinovitch Limitation Effect caused an explosion which allowed the older Susan to avert the original crash, by having her original self to suggest her grandfather to shut down the defence systems of the ship. (AUDIO: Tick-Tock World)

Undone events
When the Cybermen allied with to take over history, (COMIC: Supremacy of the Cybermen) three Mondasian Cybermen captured the First Doctor at 76 Totter's Lane on Earth in November 1963. (COMIC: Prologue: the First Doctor) This timeline was eventually unwritten by Rassilon and the Twelfth Doctor. (COMIC: Supremacy of the Cybermen)

In a negated timeline, the TARDIS was attacked on 23 November 1963 by a conceptual bomb bought by and began to be erased from time. The First Doctor, along with his second and third incarnations, became trapped in another dimension, and tried to warn their other incarnations by reducing the explosion to a blinking light on the TARDIS with the coordinates of the explosion. However, when their four successors followed the warning, the Master took direct action in attacking them, until the Sixth Doctor managed to bring them together to formulate a plan. After the Fifth Doctor ensured that the TARDIS would not explode, the Doctors prepared to time ram the Master's TARDIS. However, rather than kill the Master, the First Doctor instead turned off the automatic distress actions, making it so none of the Doctors followed it into the explosion and undoing the events of the day. (AUDIO: The Light at the End)

After departing Troy with Steven Taylor and Katarina, the TARDIS collided with its future self and landed on Urbinia. The Doctor settled on the planet for three months among the scientific community, delivering lectures while hoping to fix the TARDIS's circuits. In his absence, however, the Daleks developed the Time Destructor and attacked the planet. The Doctor effectively took charge of the evacuation, but came into conflict with his second incarnation, who warned him that Katarina had to die to prevent the Dalek conquest. The First Doctor was ultimately captured by the Daleks, but the Second Doctor flung his TARDIS back into the heart of the initial collision, preventing it. The First Doctor arrived on Kembel and the timeline was reset. (AUDIO: Daughter of the Gods)