Mara Jade, one of the most well-known and important characters in stories now considered Legends, has been an assassin, a smuggler, and a Jedi Knight. She worked for Emperor Palpatine, she married Luke Skywalker, and she and Luke had a son named Ben (yes, Ben).
Mara Jade debuted in the Timothy Zahn novel Heir to the Empire. She appeared numerous comics and books including books in the following series: The New Jedi Order, Dark Nest, Legacy of the Force, and Fate of the Jedi. (See her Wookieepedia page for a good list of all of her appearances.)
If you’re looking for a brief history of her character this video from Star Wars Minute is for you.
Comic Vine has a good visual list of comics Mara Jade appeared in.
Mara Jade won a fan’s choice action figure poll in 2011. Here’s her Black Series figure.
And because I really like this You Tuber’s Scottish accent, here’s another video about the life of Mara Jade.
Check out the entire list of women in 365 Days of Star Wars Women in the Women in Star Wars Index. It includes highlights from each post plus notes which posts include new 365 interviews with actresses, writers, artists, and more.