Child Master (The Then and the Now)

At some point during the Last Great Time War, the Master worked with the War Doctor and the Squire, until an attempt to flee the conflict resulted in his personal timeline being aborted in a paradox, returning him to his.

Biography
At some point, the Master regenerated into a new incarnation. Now in the body of a small child, (COMIC: The Organ Grinder) the Master, as he always did after a regeneration, visited the Scoundrels Club. (PROSE: Dismemberment)

Alliance with the Doctor


The Master fought further along in the Last Great Time War than his predecessor. Despite this, he was able to manipulate events to write out many of his actions during the War, even though it was timelocked. (COMIC: The Judas Goatee) The Master made a deal with the War Doctor to end their old ways of fighting to become allies, fighting alongside the Doctor and his companion, the Squire during the period of the War in which the Cyclors allied themselves with the Daleks. (COMIC: The Organ Grinder)

The Doctor and the Master travelled to Veestrax, where they saw a broken wall with "Exterminhate" written on it. The Master told the Doctor that he hadn't written it. The Doctor then asked for the Master's help with destroying the planet. (COMIC: Outrun)

He arrived on Golgauth with the Doctor, asking what he intended to do, to which the Doctor said "what [he] [had] to". (COMIC: The Then and the Now, The Organ Grinder) The duo soon encountered the Volatix Cabal, together killing one of its members. They then encountered Alice Obiefune, who had travelled in the Master's TARDIS from after the War had ended. The Master set about tethering his future TARDIS to the Doctor's while the Squire set about saving Alice from the Volatix Tendrils.

With both TARDISes in tow, they travelled beneath the surface of Golgauth, where an Overcaste rebel base was located. The Master and the Doctor revealed a Volatix spy in the group and neutralised him. The spy revealed that he had called for help and moments later a Cyclor tore off the roof of the base. (COMIC: The Organ Grinder) The Master used a device to summon a squadron of Gallifreyan ships to attack the Cyclors. He used this chaos of the Cyclor attack to flee, sneaking into his future self's TARDIS to escape the Time War.

However, he discovers that it was his future self that implanted the chronal tumour on his console in the first place. At some point in his now aborted future, he was to operate on the brain of his TARDIS, which would result in the chronal tumour that protruded from one side of the console. (COMIC: The One) But since escaping the Time War in his TARDIS would preclude him from implanting the tumour in the first place, the resulting paradox shattered reality in "a cascade of temporal possibility." Subsequently, the chronal tumour began to react to the Psilent songbox. While the Master attempted to disarm the device, it was too late, and the resulting temporal bomb left the time-ship spiralling out of control. With the Master's timeline collapsing as a result of the paradox, Alice's intervention in the War and the life he now never led was erased, leaving the Master, reverted to his previous incarnation, fleeing the event horizon of the temporal bomb. (COMIC: Fast Asleep)

Psychological profile
While fighting in the Last Great Time War, the Master delighted in the prospect of committing genocide. He saw people as resources, and that teaming up with the War Doctor was a worthwhile option during wartime. He also had a fondness for paradoxes. (COMIC: The Organ Grinder) The Master wanted to fight in the Time War, but seeing the hopelessness of his efforts with the Doctor he fled from their fight with the Cyclors. He concluded that he enjoyed death and chaos only when it was fun for him. (COMIC: Kill God)

At the moment of his retro-regeneration, the Master held contempt for the Doctor and Alice Obiefune, declaring that he would have his revenge on them. (COMIC: Fast Asleep)

Appearance and clothing
In this incarnation, the Master's body was that of a small child with black hair and blue eyes. (COMIC: The Organ Grinder) On Veestrax, he had short hair, and wore a white shirt with a black jacket. (COMIC: Outrun) By the time he and the Doctor had arrived on Golgauth, the Master's hair was longer, and he sported a scarlet shirt under his jacket. (COMIC: The Organ Grinder)

Behind the scenes
Although Fast Asleep (the last regular story to feature this Master) includes a panel which visually resembles a traditional regeneration, Rob Williams, who wrote the comic, clarified that the "Child" Master was intended to be the successor of the War Master, rather than his predecessor.