The Doctor had tried to stop Chaos in many incarnations only to fail and be killed. The Ninety Ninth Doctor was mortally wounded when Chaos attacked his TARDIS damaging the console inside but also hurting the Doctor. The mortally wounded Ninety Ninth Doctor then regenerated into his One Hundredth Incarnation. After regenerating for the ninety ninth time, The Doctor wasn't used to his new body and was suffering from Post Regeneration trauma so he collapsed into a comatose state. The Doctor woke up after having been in a comatose state and then remembered he was supposed to save the universe from Chaos. On Earth he teamed up with a futuristic UNIT in the year 6092 and met Brigadier Ki Nona who was a Silurian. Ki became the doctors new companion and together they attempted to stop the personification of Chaos. Finally they destroyed Chaos which seemed shocking and impossible, only to figure out it was The Master who had been dying many years ago and transformed into a god like being to feed on planet's life to stay alive longer. After this the universe was back to normal and Ki departed, leaving the doctor alone (DW: Chaos Spreads).