As with most of the naaru, little is known of A'dal personally, though he appears to count Khadgar and Velen as personal friends. At some point following the destruction of Draenor, A'dal and his compatriots, the Sha'tar, arrived and assisted the Aldor in reclaiming the ruins of Shattrath City. A'dal also approved an alliance between Shattrath's forces and the Sons of Lothar, to the extent that Khadgar moved to Shattrath to assist the Sha'tar.
At some point after Illidan's victory over Magtheridon, an army of blood elves marched on the city. But instead of laying siege to Shattrath, their leader, Voren'thal the Seer, kneeled before A'dal and pledged the support of his forces, the Scryers, to the cause of A'dal and the Sha'tar.
At some point prior to the blood elves' assault on Tempest Keep, Velen made a cryptic prophecy concerning the redemption of a people cursed by blood. A'dal and the other naaru realized what was to come, allowing M'uru to be captured by Kael'thas Sunstrider's forces and sent back to Silvermoon to power the Blood Knights. Ultimately, the prophecy was proven true when M'uru was again kidnapped by Kael, this time stealing him away from his own people. With the entirety of Kael'thas's betrayal now exposed, Lady Liadrin journeyed to Shattrath City to beg the naaru's forgiveness. A'dal revealed the nature of the prophecy and assured the Blood Knights that the naaru harbored no ill will towards them. Liadrin promptly re-dedicated the Blood Knights to furthering the cause of the Sha'tar and stopping their former Prince once and for all.
In Icecrown, Crusader Bridenbrad is struck with the Plague of Undeath during the assault on Scourgeholme. Tirion Fordring sends willing adventurers to Remulos, Alexstrasza, and eventually A'dal in an attempt to save Bridenbrad. After completing the quest, Crusader Bridenbrad ultimately dies, only to have A'dal appear along with two other naaru: K'uri and M'ori. A'dal personally tells the adventurer that "The Light does not abandon its champions.", and instead of becoming a mindless undead ghoul for the Lich King, Bridenbrad "shall taste only paradise".
While it is very difficult to engage him in combat, some enterprising players have managed to kite enemies into Shattrath and use them to attack A'dal[1]. In the past, A'dal has actually been killed by some of these attacks, but as of Patch 2.2, A'dal has apparently been buffed and now hits for over 100,000 damage per attack on Fel Reavers. A'dal becomes invulnerable at low health, to make him stand Varedis' attack (who also becomes invulnerable at low health).