And you thought the Zahn books go way back? Grammel hails from 1978's first ever Expanded Universe content, Splinter of the Mind's Eye by Alan Dean Foster. In 1995, the book was adapted as a Dark Horse comic book, sans the creepy hints of sexual tension between Luke and Leia. Grammel functioned as their main Imperial antagonist until Darth Vader's inevitable arrival.
As the most forgettable character on this list, Grammel's obscurity excellently represents how deep LucasArts dove for officers in Rebellion, its 1998 PC strategy game that was a bit impenetrable due to overwhelming depth and complicated interface. Want some other examples of characters you've never heard of? Try Huoba Neva (Dark Horse's Dark Empire), Pter Thanas (The Truce at Bakura by Kathy Tyers), and Kaiya Adrimetrum (The DarkStryder Campaign, a tabletop role-playing game by West End Games). There are many more.