Ajani Goldmane was one of the first five planeswalker cards, printed in Lorwyn. We knew little about him, as the Lorwyn 5 didn't actually show up in the storyline of Lorwyn, but he was interesting in that he was a grizzled and battle-scarred leonin with abilities that didn't really fit that sort of image - mostly he was about healing and protection.
We didn't have to wait very long to get Ajani's origin, however. He was born on Alara, a plane that had long ago been split into five pieces called shards. Ajani was from Naya, a jungle covered shard linked to white, green and red mana. Due to being born an albino with white fur, Ajani was shunned by all the other leonin, aside from his brother Jazal. Not even his royal blood (Jazal was kha, or king, of the leonin) saved him from their derision.
The five shards of Alara were on a collision course with each other. When they collided, Alara would be reunited, but a nexus of powerful energy called 'the Maelstrom' would be formed. The ancient dragon-planeswalker Nicol Bolas was dying of old age, and, believing the nexus could restore him, enacted a plan to empower it. If the inhabitants of the shards went to war with each other, the excess energy of spells that they cast in battle would be gathered by the Maelstrom. there were a few obstacles to his goal - one was that Jazal was a rather moderate leader, unlikely to be drawn into a war. Furthermore, he may have convinced the elves and humans of Naya to remain neutral as well.
So Nicol Bolas had Jazal assassinated. His plan succeeded (Naya did later go to war), but he inadvertently made an enemy of Ajani, whose spark ignited due to the trauma of his brother's death. Planeswalking to another shard - Jund - Ajani met the planeswalker Sarkhan Vol, who explained to Ajani that he was a Planeswalker. Sarkhan (sounding very Sith) encouraged him to take hold of his anger and use it to track down his brother's killer. He also showed Ajani how to planeswalk back to Naya.
Whilst on the trail of Nicol Bolas, he was attacked by another leonin and severely injured. Planeswaking away, he found himself on another shard - Bant - where he was rescued and healed by a third planeswalker, the knight-errant Elspeth Tirel.
Eventually Ajani, with the help of a combined army of elves and leonin, managed to track down and confront Nicol Bolas. Bolas absorbed the Maelstrom Nexus, restoring his youth and much of his power. But he underestimated Ajani, who blindsided the elder dragon by absorbing the remeining energy of the Maelstrom and using it to create a reflection of Bolas that banished the dragon from Alara forever.
At some point after the events of Alara, Ajani joined an unofficial group of planeswalkers that also included Tamiyo, Elspeth and Narset. Dubbed the 'Story Circle' they travelled the multiverse collecting stories.
Elspeth was a rather broken soul, having been tourtured by Phyrexians when she was young (which would make her one of the oldest living planeswalkers). But Ajani felt he owed a debt to Elspeth for healing him. After failing to get her to return to Bant from a self-destructive sojourn on Dominara, he followed her to the plane of Theros. Though he helped her succeed on her quest to defeat the evil planeswalker/god Xenegos, he was unable to prevent her from being killed by the sun god Heliod. But this time Ajani's vengeance took a very different form. Donning Elspeth's iconic cloak, he traveled the length and breadth of Theros, telling all about the bravery of Elsepth, and about the betrayal of her supposed patron Heliod. The gods of Theros derive their power from their worshipers, and Ajani's tales have turned many away from following the sun god.
Eventually Ajani felt the story of Espeth had become widespread enough that it would continue to be told without him, and he left Theros, travelling to Kamigawa to tell Tamiyo of Elspeth's death, and giving us the awesome scene of Tamiyo's little children clambering all over Ajani demanding he tell them stories.
But Ajani had one more task to take care of - Elspeth had told him of the planeswalker Tezzeret's actions on New Phyrexia, so when Tamiyo told him of crimes committed by his followers on Kamigawa, Ajani decided to track down the renegade artificer and bring him to justice. Tracking Tezzeret to the plane of Kaladesh, Ajani fell in with the Gatwewatch - a group of planeswalkers consisting of Gideon, Jace, Liliana, Chandra and Nissa - and helped them defeat the oppressive Kaladeshi Consulate, but not before Tezzeret revealed he was working for Nicol Bolas, and made of with a powerful 'planar bridge', which would allow Bolas to transport objects between different planes.
Although the Gatewatch wished to confront Bolas immediately, Ajani was no fool, and admitted that while he had defeated Bolas in the past, the elder dragon had been caught off guard, and would not be defeated so easily again. Ajani left to find others to help fight the dragon. Meanwhile, the Gatewatch ignored him, and...well...lets say that ended badly for them...
