Allin is dark-haired and wears a beard shaved at the sides.
Allin is fighting in the Last Battle under Uno's orders by the time Demandred arrives to the field. Allin is allegedly a character created in this fan's likeness: https://www.goodreads.com/author/show/12063299.Eric_Allen
"Also, some time ago, Brandon Sanderson ran a charity fundraiser. For a mere ten dollars, a person could have their name and general description entered into a drawing. These names would be pulled out whenever Sanderson needed to give a character a name. He would try to work in the person's description as much as possible, and change the person's name to fit within the world of "The Wheel of Time". Much to my surprise and childlike glee, my name was drawn the very day that I entered it. In the chapter titled "The Last Battle" on page 626, a little more than halfway down, you will find a character named Allin being yelled at by Uno who shares my general description. That's where I was used. Amongst the best ten bucks that I've ever spent, I think."