User blog comment:Godisme/Foundation Stones/@comment-4515326-20120322092924/@comment-3521993-20120328175330

I believe that Ivan was/is a Quincy who died, became a hollow and so Aizen made him into an Arrancar. Since Hollows keep some personality of their former spirit, it's easily possible that Quincies can become Arrancars. Through this, Aizen probably wanted to do the same as the Vandenreich through Ichigo, but it didn't go well. For Harribel, it's likely the case that Buckbeard (What I call the leader) has used Harribel to create Arrancar, throuh her Resurreccion, judging by what he has said. True about Sasakibe. He was kind of like a teacher's pet, and one of only 4 non-captains to get Bankai. That shows, that he is stronger than every other Lieutenant, with the possible exception of Renji.