U-Dan is a supporting character in Skeleton Men of Jupiter.
Five years prior to the events of the story, he was a padwar in the personal guard of Zu Tith, the Jed of Zor. Although his honor forced him to fight for Zu Tith, he actually hated him and his cruel reign. After Helium conquered Zor and Zu Tith was killed, U-Dan swore loyalty to John Carter.
U-Dan was in love with Vaja, the cousin of Zu Tith's son Multis Par. When Multis Par was captured by the Morgors, he came up with a plan to get revenge on John Carter. He had the Morgors abduct Vaja so he could force U-Dan into helping him capture Carter. U-Dan does so, but feels terribly sorry for it and apologizes to John Carter after he is taken captive. He tells John Carter all he knows about the Morgors.
Along with John Carter, U-Dan is imprisoned on Sasoom. The two men make friends with the Savator Zan Dar and the Morgor Vorion. Together they escape from their prison, steal a ship, and free Vaja and Dejah Thoris (who at this point had also been brought to Sasoom). John Carter is captured again when he fights Multis Par, but U-Dan, Zan Dar, Dejah Thoris, Vaja and Vorion manage to escape to Zan Dar's homeland Zanor.
U-Dan is not seen again in the rest of the book. At the end of the story John Carter arrives in Zanor and expects to be reunited with Dejah Thoris, but it is not revealed if she and the others are actually there.