Dragon War and Ascension
The chronologically oldest bit of Magic lore we have is that about the Elder Dragon Wars, a conflict that shook the planes and killed most of their kind, some twenty-five thousand years before the Brothers' War, The Elder Dragons were ancient dragons of Dominia. Their vast power rivaled that of planeswalkers. Nicol Bolas emerged victorious and during this time became a planeswalker. The other know survivors of the Dragon Wars are Nicol Bolas’ siblings; Chromium Rhuell, Arcades Sabboth, Palladia-Mors, their cousin Vaevictis Asmadi and possibly Piru. The winners of the war became the ancestors of all dragons and drakes, while the losers were stripped of their wings, limbs and most of their power and became the Elder Land Wurms, which spawned all other wurm species. Viashino are also descendants of them, although it is unknown how.
Some thousands of years later, Bolas fought against a demonic leviathan in the first duel between planeswalkers on the still-young plane of Dominaria. The fight lasted a month, reduced Madara to a third of its former size, and created the first rift. In the end the dragon used his magic to defeat his foe. After the battle Bolas feasted on the remains of the leviathan over the course of a year, absorbing its power in the process. When he finished, not much was left of the leviathon corpse besides what eventually became known as the Talon Gates.
On Madara three mana lines, blue, black and red, intersect at a single point. The empire was founded by a warrior-queen who styled herself a god-empress. Because of the three mana lines that met, Nicol Bolas thought Madara would be a good place to start a foothold on Dominaria. Bolas was such an ancient planeswalker that he needed a strong base of his main colors to remain on a plane for long. The dragon took the empire, becoming a real god-emperor. Bolas took over the Empire of Madara and erected his Imperial Shrine on this focal point.
The Imperial Shrine was the place where the highest ranking officers in the Madaran Empire had their audiences with emperor Nicol Bolas. The elder dragon needed tremendous amounts of mana to stay on a plane for long, so he usually only manifested partially in the shrine, which was located in the middle of three strong mana lines: blue from the Suido River, black from Madara’s various swamps and red from the Gitte-Yatay Mountains.
Connection to the plane of Kamigawa
For around 400 years Bolas ruled Madara through three individuals: the imperial assassin, the imperial champion, and the high general of the kentsu army. The dragon later realized this system was becoming obsolete as assassin Ramses Overdark was successfully replacing the other imperial officers with his own minions. Bolas then made a new system with only one placeholder of the emperor: imperial regent Ramses Overdark.
Tetsuo Umezawa was the imperial champion of the Empire of Madara around the time of the Mirage War. Tetsuo was a distant descendant of Toshiro Umezawa, ender of the Kami War. Toshiro Umezawa was exiled to the coast near the Talon Gates at Madara, Dominaria. He was trained in many martial arts and magical techniques and was arguably the most powerful human of his time. Raised with a strict honor code, he was oft torn between his honor and his master, the vicious emperor of Madara, Nicol Bolas. Tetsuo renounced his title of champion and swore vengeance. In the following weeks Tetsuo spent most of the time training on the Meditation Plane, where Bolas couldn’t find him.
After being promoted to imperial regent Ramses Overdark stayed in the Shrine, and it was there that he fought, and lost, his final battle against Tetsuo Umezawa. The Shrine was destroyed shortly after that by Tetsuo’s Meteor Hammer spell. When the dragon chased him, following him to the Meditation Plane, he was killed by Umezawa in his weakened state. A remnant of his life force still lingered in the rift by the coast. This resulted in the exile of Nicol Bolas, destroying that system as well. After this the empire plunged into chaos, with various nobles buying parts of the kentsu as their personal armies and oppressed islands and tribes rebelling. Tetsuo set out to restore balance to the empire, but how this ended was never revealed. Madara is currently overrun with the cat-dragon race, the nekoru. The humans of Madara exist solely as servants, clerics, and slaves.
Bolas remained present in his land during the time rifts, existing under the name of Sensei Ryu. His home was overrun by cat-dragons (nekoru) and their followers. When he sensed that Teferi was lost in a rift and had left behind his companions he arranged for them to arrive on the Madaran beach near the Talon Gates. Using Venser's spark he was able to escape his prison and was reborn. After Teferi located his companions, he challenged the dragon to a duel in an effort to stay his revenge. Bolas easily won, but when Teferi shared his thoughts with him he saw the severity of the rifts. He quickly left and swore a vow to devour take vengeance by destroying on anyone related to the Umezawa line, and anyone who had ever come into contact with it, then presumably left to Kamigawa.
Bolas returned to Madara, where he was ambushed by Leshrac, who challenged him to a planeswalker duel; the later was defeated and imprisoned in the mask of the Myojin of Night's Reach. It was implied by Bolas that he had stripped most of that spirit's powers but she had managed to escape.
After closing the Madaran rift, Bolas left for a plane of his own devising, separated from the rest of multiverse. He escaped there, believing that nothing could stop the collapse of the multiverse. Although the multiverse survived, Jeska's Mending spell changed the nature of the planeswalker's spark, making Bolas the last true planeswalker known to exist.
It is unknown if he will ever reappear as a character since his plane was going to be isolated from the rest of the Multiverse. The current theory is that this plane of his own crafting may be Grixis, one of the Shards of Alara.
For more information regarding the recent exploits of Nicol Bolas, please read this article on the mother ship.