Arrancar (破面（アランカル）, arankaru, Japanese for "broken mask", Spanish for "to tear off") are hollows that have had their masks almost completely removed and--through this process--gained the powers of a Soul Reaper, a more humanoid appearance, as well as strength, speed, and intelligence beyond the level of a normal hollow.
In addition to those improvements, arrancar also gain hierro (鋼皮 (イエロ), iero?, Japanese for "steel skin", Spanish for "iron"), skin so hard that it allows them to fight against sword-wielding opponents bare-handed, but is by no means impenetrable. In order to travel at extremely high speeds across short distances, arrancar use a technique known as sonido (響転（ソニード）, sonīdo, Japanese for "transfer effects", Spanish for "sound"). Stronger arrancar have been shown to possess proportionally harder hierro and faster sonido, among other abilities, either unique or based on common techniques, such as the several existing variants of cero.
Like Soul Reapers, arrancar possess zanpakutō (斬魄刀, lit. soul-cutting sword). Unlike Soul Reapers, whose zanpakutō are manifestations of their owner's soul, arrancar's zanpakutō are manifestations of their former hollow selves. With occasional exceptions, an arrancar's zanpakutō resembles a regular sword in its sealed state. When released through a process called resurrección (帰刃（レスレクシオン）, resurekushion, Japanese for "returning blade," Spanish for "resurrection"), part of their original hollow form is restored, changing their appearance, giving them greater strength, and granting them access to their original abilities.
Arrancar become major antagonists during the second part of the series as they start being led by Sōsuke Aizen, who uses the Hōgyoku to create and perfect the arrancar. According to Tite Kubo, many of the arrancar are named after real life architects and designers.