Board Thread:Questions and Answers/@comment-13442349-20130726072748/@comment-26420452-20131103203949

We've never seen in canon how a Vasto Lorde is supposed to look like, it's just been stated they are more or less the size of a human.

Arrancar have existed long before Aizen came around in Hueco Mundo. They became so by simply tearing off their masks, however they were incomplete and few in number. With the Hogyōku, Aizen managed to make an army of complete Arrancar.

However, even when they've become a complete Arrancar (and so the most Plus they can ever be), they tend to show Hollow behaviour, apart the two Espadas I mentioned. And by the way, Harribel is Espada #3.