My OC Moses Blaccthrope's appearance as a Vasto Lorde-class Hollow.
Blaccthrope was the strongest and most trusted of all King Baraggan's army, as such he was given the honor of second in command and his own extermination squad to lead: (A group of Hollows Baraggan would send to track down and annihilate those who rebelled/wouldn't obey him).
While he was away dealing with a group of rebels he was unaware that his Lord's kingdom had been invaded by the Shinigamis Aizen, Gin and Tousen.
By the time he returned he was shocked to discover that Baraggan had been defeated and Aizen was using his Army as slave labor to begin construction on what would eventually be known as Los Noches, on top of the very grounds which Baraggan once called his Kingdom.
Seeing his King's wrapped up body kneeling next to his former throne (which Aizen now occupied, having begun the process of transforming Baraggan into an Arrancar) was too much for Moses to bear and he moved to attack the trio.
Underestimating him Gin casually fired his Shikai at him but the powerful Hollow had no problem deflecting such an attack with his armor.
Impressed by his courage and strength Aizen offered him a chance to join them, to which he refused.
Intending to "Break" him Aizen commanded Gin to test the Hollow's power, despite his strength the battle was over quickly once the Shinigami released his Bankai.
Moses had no choice but to submit and was transformed into an Arrancar just like his King, due to his power he was made a member of Aizen's original Espada, but behind the scenes he would continue to serve only Baraggan and the two of them plotted their revenge.
Moses's Arrancar form: