Ulquiorra is a male arrancar with a melancholic appearance. Ulquiora is the 4th ranked espada.
Ulquiorra is also analytical; during his and Yammy's first visit to the human world, he makes several remarks on the humans who confront them. He theorizes that Orihime Inoue's healing power is a temporal-spatial ability, which Aizen describes as the rejection of fate, and comments on how Ichigo Kurosaki's final release can easily get through Yammy's defenses. He also notes Ichigo's power fluctuation, which varies between very weak and stronger than his own.
It would appear that Ulquiorra and Grimmjow, the 6th Espada, are not on good terms. While Ulquiorra allowed Yammy to kill anyone he deemed as "trash", which included Ichigo, Ulquiorra allowed him to live based on his belief that Ichigo's power was so turbulent that eventually he would destroy himself. Grimmjow's conflicting viewpoint was that Ichigo should have been destroyed outright, as he could overcome his weakness and grow even stronger. Despite Grimmjow's argument, Aizen trusted Ulquiorra's judgment. This disagreement led to Grimmjow's unauthorized assault on the real world. Though Ulquiorra is of a higher rank than Grimmjow, Grimmjow is confident that Ulquiorra is afraid to fight him for fear of them destroying one another.