General Demoux was a Captain in Kelsier's army, and later a general in Elend's. Demoux fights a man who believes that Kelsier's rebellion will fail during the first book, and is helped by Kelsier's Allomancy. Despite being almost a member of the crew, Demoux sees Kelsier as a god and is a preacher in the Church of the Survivor.
It has also been confirmed, by Brandon, that Demoux is also a world hopper, along with Galladon and Hoid, and can be seen in the interludes in The Way of Kings as the man (with the scar) searching for Hoid/Wit.
Sidenote: He was named for Brandon Sanderson's friend, Micah DeMoux, who allowed Brandon to use the name only if his character could "survive and get a girl". Incidentally, Micah is also the person who took Brandon's author photo. See the photo credit on the book.