Dash Rendar and Prince Xizor
It's debatable whether or not these two belong on this list since their first appearance in a book was created in tandem with a game – so let's just say this about Shadows of the Empire (1996): You might remember it best for selling you an N64, or maybe it was the first game you played on PC that required a 3D graphics card. But what else were this bounty hunter and space gangster known for when it came to games? Just a few things…
One mission in X-Wing: Alliance adapted a chapter from Steve Perry's Shadows of the Empire novel word for word, as the player followed Rendar's Outrider and Luke Skywalker's X-wing into a space battle. The action dovetailed nicely with a later level in the Shadows game, as Rendar infiltrated a freighter called the Suprosa.
And Xizor? If you thought his appearance in the Shadows game was minimal, just wait till you (don't) see him in Empire at War: Forces of Corruption, brokering a deal with the game's shady protagonist, Tyber Zann.
Interestingly, neither Rendar nor Xizor have survived outside of Legends, though core pieces of them actually do exist as part of current canon: Rendar's ship, the Outrider, can be seen departing Mos Eisley in A New Hope, while Xizor's crime syndicate, Black Sun, appears all over the books and animated series.