User blog comment:Kamikaze839/Kami's Character Analysis 2: Baraggan Louisenbairn/@comment-44061-20140122170741/@comment-3177945-20140123182605

I'm guessing he looked so similar before Aizen and in ressurection because he was a Vasto Lord that peaked his abilities, and thus already had a humanoid form. Although nothing has been stated, it is fairly deductable that up to the 4 Espada they were all Vasto Lord (being turned afterwords by Ainzen or naturaly), since it was a rule that only those could not release in Hueco Mundo, indicating a bigger gap between 4 and 5