Hooleer

This Giant Unnamed Hollow is a large entity that appears to be fighting alongside Sōsuke Aizen. The true nature of this creature remains unknown, but it seems connected with Gillian-class Menos, sugesting him being a Hollow.

Character Outline
It has a bulbous body, long tufts of hair on its back and a large single eye. Its hair appears to be the same or a similar color to its skin. It also has the masks of Gillian-class Menos for toenails. It made a slight appearance early in the series, but recently made its proper debut during Aizen's invasion of the Fake Karakura Town. It is arguably the largest creature yet seen in the series.

Soul Society arc
It first makes a short appearance as Sōsuke Aizen, Gin Ichimaru, and Kaname Tōsen are being extracted from Sōkyoku Hill via Negación. Its eye can briefly be seen behind the mass of Gillians present within the Garganta, but the rest of its body remains hidden.

Fake Karakura Town arc
Wonderweiss Margera appears during the Gotei 13's battle with the Espada, bringing the creature with him. It is evident that it dwarfs the other combatants. While Wonderweiss attacks Jūshirō Ukitake, the Hollow uses its breath to extinguish the fire prison that is trapping Aizen, Ichimaru and Tōsen, thus freeing them. After Wonderweiss screams, it releases Gillian's from his mouth to attack the Vizards.

Powers & Abilities
Breath: The Hollow's breath is powerful enough to put out the prison of fire made by Genryūsai Shigekuni Yamamoto's zanpakutō's ability, Jōkaku Enjō (though it must be said that they had already been burning for some time at this point). It is implied that it "smells of death". Whether this means it has other more obscure effects remains to be seen.

Menos Manipulation: It is shown to be able to summon numerous Gillian Menos from his mouth. At first, it looks like a mass of black liquid, until the Gillian Menos separate into their individual forms.

Appearances in other Media
This giant creature appears as one of Aizen's special moves in Bleach: Blade Battlers 2nd, where he spits out Gillians to attack.

Trivia

 * While the name for this Hollow is still unknown, many fans refer to it as Superchunky due to the fact that this Hollow was first fully introduced in the chapter titled "Superchunky from Hell".
 * It is so far the only Hollow to not have a hole.
 * So far as can be seen, this Hollow also appears not to have a hollow mask as such beyond having Gillian masks as fingernails.