Grimmjow has light-blue spiky hair and eyes, and also has green lines below them, similar to the eye markings on thePanthera genus of cats, as well as the red marks on Ikkaku Madarame's eyes. Grimmjow's attire consists of a white hakama and a black sash; his white jacket is ragged with an upturned collar. The inner lining is black, the sleeves are rolled up, and Grimmjow wears it open, leaving a muscular chest revealed. The remains of his Hollow mask consist of the right jawbone, and his Hollow hole has moved to his abdomen. His tattoo number (6) is located at his back, near the right side of his Hollow hole. Since his first fight with Ichigo, Grimmjow sports a large scar on his torso, which several characters make remarks to.
Grimmjow appears to be a laid-back and irreverent individual at first glance, but this scruffy exterior hides a brutal, impulsive, excessively-violent personality and a lethally-short temper. Grimmjow is blunt, sarcastic, and quite sadistic, revealing a psychotic grin whenever he becomes excited, much like Kenpachi Zaraki or Hollow Ichigo. He displays little respect for authority and says whatever is on his mind, regardless of whether or not it is appropriate. This attitude leads to conflicts with Kaname Tōsen, who holds Grimmjow in the same low regard as he did with Kenpachi Zaraki. He also has conflicts with Ulquiorra Cifer, the 4th Espada, usually because Ulquiorra interrupts his battles or otherwise clashes with Grimmjow's ideals, and confidently believes Ulquiorra's powers to be weaker than his, a point he is eager to prove. He develops an additional grudge against Ichigo Kurosaki for wounding him during their first and second fights, and is eager to return the favor. He intentionally kept the large scar on his chest from their first battle as a reminder of this. Grimmjow is also infuriated by Ichigo's belief that he can defeat him regardless of how badly he is injured, which Grimmjow sees as Ichigo looking down on him.
Grimmjow is a very rude and disrespectful character. He uses none of the honorifics in the Japanese language, except when addressing Aizen (though he is quick to discard the formality when Aizen is not around), and refers to Orihime as woman in conversation. However, he does have some form of a code of honor, as he is unwilling to fight an injured Ichigo, bringing Orihime to heal him beforehand so that their battle will be a fair one, though he also wants to defeat Ichigo when he is at full strength. He also saves Orihime from Loly Aivirrne and Menoly Mallia, who were beating her up, to repay the debt of restoring his arm, though he immediately demands another favor afterwards. Despite his aggression and obvious bloodlust in battle, he possesses a feral cunning and has a knack for quickly exploiting any opening his opponent reveals.
Before Grimmjow became an Arrancar, he was a panther-like Adjuchas-class Menos. At one point he came across the Adjuchas-class Menos group of Shawlong Kūfang, Edrad Liones, Yylfordt Granz, Nakeem Grindina, and Di Roy Rinker. Di Roy decided to eat him but before Di Roy could act, Grimmjow attacked him and ate a chunk of Di Roy's head. The group was impressed at his strength and they introduced themselves. Their leader Shawlong asked that Grimmjow join them, and the group bowed to him. Shawlong then explained that they have no intention of remaining Adjuchas or Gillians. They vowed to become Vasto Lorde, but in order to do that they needed strength that they can use to pull themselves up, and they had seen that strength in Grimmjow. Shawlong asked that Grimmjow lead them as their king.
Sometime later Shawlong told Grimmjow that the group has given up. Yylfordt explained that they have given up in their quest to evolve into Vasto Lorde. They had eaten over one thousand Hollows and haven't felt their power increase anymore. As of that day they had eaten three thousand so they know for certain to continue on would be pointless. Grimmjow told them that if they wanted to give up then it was fine but he would have nothing to do with it. Shawlong then asked Grimmjow if he would eat them, and noted that since Grimmjow had already taken a piece of Di Roy, he would never evolve into a Vasto Lorde and that in conjunction their evolution would end where it was at as well. Grimmjow called them cowards but Shawlong interrupted him and explained that they have become enlightened. It is not only to the fact that they would never become Vasto Lorde, but it was something they knew even before becoming Hollows. They knew that they would always only be Adjuchas and that Grimmjow would have been the only one to evolve beyond that stage.
His release command for his Zanpakutō is "Grind" referring to grinding one's teeth. To release his Zanpakutō, he holds it up, like the start of a low sweep stroke, with his right hand. The sword glows as he puts his left hand up to it. He then rakes his hand along the length of the blade, with a swift motion, while calling out its release command, in turn releasing a torrent of spiritual power that causes tremendous gusts of wind in the immediate vicinity. Grimmjow's appearance changes drastically to something more feline and predatory. His teeth become jagged and sharp, his hands turn into black claws and his feet become black clawed paws, similar to that of a cat, along with a slender whip-like tail. His hair becomes very long and flowing, and the markings around his eyes enlarge and extend to the tips of his ears, which become cat-like. He loses his distinctive jaw mask, which is replaced by a sort of a headgear on his forehead. His clothing changes to become a form-fitting white segmented armor, similar to his original Adjuchas-Hollow form. He has blades protruding from his forearms and his calves.
- Grimmjow's aspect of death is Destruction.
- Grimmjow's name stems from that of Nicholas Grimshaw, an English architect noted for modernist buildings.