Ulquiorra is a slender, yet fairly muscular, male Arrancar of average height with a melancholic appearance, fairly short, messy black hair, pale white skin, a black upper lip, and green eyes with slit-shaped pupils similar to a cat's. Part of his bangs falls between his eyes, and he has distinctively thick eyebrows. He has teal lines that descend from his eyes, making it appear as if he is crying. His facial expression rarely changes, and he is almost always frowning. He wears typical Arrancar clothes: a white jacket, black sash, and a white hakama. However, his jacket seems to have longer coattails than others, and the collar is rather high.
Like most other Arrancar, he possesses remnants of his former life as a Hollow in his appearance. His Hollow hole is located on his sternum where a heart would normally be (though initially, the hole was located on the base of his throat, a change that was seen in both the manga and anime). The remainder of his Hollow mask lies on top of his head, forming a broken helmet. He is the fourth-ranked Espada, signified by the tattoo on the left side of his chest.
Ulquiorra is a very cold, callous, dispassionate figure, and is rather aloof, brooding, and indifferent, willing to harm both his comrades and enemies should they ever get in his way. He refers to anyone he does not find interesting as "trash" and treats them as expendable. Despite this, like most of the other top Espada, he is not particularly violent and will only fight when provoked or ordered to by Aizen.
Ulquiorra demonstrates a strange habit when killing victims he is particularly interested in, stabbing them with his bare hand in the same location as his Hollow hole, as stated by Grimmjow. Whether he is consciously aware of this habit or not is unknown. During a speech to Orihime, he claims that he does not believe in Human emotions, which he refers to as the "heart," reasoning that if his eye cannot see them, then they do not exist. These words, and much of Ulquiorra's overall behavior, reflect the concepts of materialism, which also connects to his aspect of death as an Espada, Emptiness. In the last seconds of his life, he seems to finally find his own "heart" and understand feelings.