Ichibē Hyōsube/Expanded Universe

is the commanding Shinigami of the Royal Guard, holding the title.

Personality
Not much is known about Ichibē's own free will, as he is solely driven by an unquestionable loyality an obedience towards the ancestors of the five Noble Houses. Ichibē seems to be indifferent to the status of the three worlds by themselves, caring only about maintaining the status quo as he was ordered to do by the Five Ancestors, as evidenced by him berating Ōetsu Nimaiya for suggesting that the Royal Guard interfere more.

Ichibē is noted to be extremely apathic, almost to the point of sociopathy, towards the horrifying and degrading existence of the Linchpin. Even as the likes of Tier Harribel, Sōsuke Aizen, the rest of the Royal Guard, Tokinada Tsunayashiro, and even Yhwach have all expressed a disgust towards the nature of the Linchpin and the Soul King's inhuman mutilation, Ichibē is noted to discuss the subject as if merely conversing about the weather. Indeed, when Shunsui Kyōraku expressed a genuine relief that Ichigo Kurosaki did not need to be sacrificed as the new Linchpin, Ichibē callously brushed off the subject, noting that he would only have missed conversing with the Human boy.

Regardless, Ichibē has shown a rather enigmatic conviction towards the Soul King, expressing his belief that everything that happens does so only according to the Soul King's wishes.

Bleach: Can't Fear Your Own World
Millions of years prior to the Quincy Blood War, Ichibē Hyōsube came into being in a chaotic, primordial world. By his own admission, he was one of the few "exceptional" beings born during that time, alongside the ancestors of the five Noble Houses and the Soul King.

Ichibē was personally present as the Five Ancestors sealed an unresisting Soul King inside a crystal and used his omnipotent powers to split their world into three new ones: Soul Society, Hueco Mundo, and the Human World, and in the process created the cycle of life and death. Ichibē likewised witnessed the Soul King's degrading mutilation at the hands of the Five Ancestors, a process he was unfazed by. For the following millions of years, Ichibē dutifully protected the linchpin and the status quo as he was instructed to do by the Five Ancestors.

At some point in the primeval days of Soul Society, a powerful Hollow attacked Soul Society and even defeated a young Genryūsai Shigekuni Yamamoto before attempting to devour the Soul King himself. However, the Hollow was defeated by Ichibē, who used his Ichimonji to erase the Hollow's name. Since the Hollow contained too many consumed Souls to purify at once, Ōetsu Nimaiya sealed the Hollow inside a Zanpakutō, and Ichibē used Shirafude Ichimonji to rename the Hollow as Ikomikidomoe.