Vasto Lorde are among the most mysterious beings who live in Hueco Mundo as they are deemed to be very rare. In the Manga, none of the Espada or Arrancar are confirmed to be Vasto Lorde. Episode 284 reveals that Tier Harribel was a Vasto Lorde Menos Grande before being recruited by Sōsuke Aizen and turned into an Arrancar for his army. There is some information in the Masked Databook that supports this but the Manga has not stated it.