Carmen Sandiego is the star of 2 games shows, a Saturday morning cartoon, a board game, and 11 video games. She is also the most badass thief ever.
Carmen Sandiego is the leader of Villain's International League of Evil, also known as V.I.L.E. Most V.I.L.E. agents have punny names such as "Baron Grinnit" and "Jacqueline Hyde". Carmen and her V.I.L.E. henchmen steal the most mind-boggling things of all time and hide them in equally weird places. Carmen Sandiego is a good sport and leaves clues behind, because nobody's going to notice that Carmen hid the Golden Gate Bridge in the Sahara Desert.
How the hell did we miss that?
It is up to ACME Agents to find Carmen and get the loot back. ACME agents are usually kids, because ACME apparently doesn't know what child labor laws are. In the game show Where in the World is Carmen Sandiego, one such child detective proved she was the most hardcore agent at ACME when she fucking broke her arm trying to catch Carmen Sandiego. Rumors stated that she later said, "I was only one day away from retirement." Another agent was sent in to catch Carmen, but she of course got away.
Carmen Sandiego hated being a kid. We learn this because of the fact she never wants to talk about it. We do know that she was a child prodigy that won a game show called It's a Wise Child when she was 10 and then she spent the next two years travelling around the world. She apparently learned to resent the world in this time.
Carmen was also one of ACME's best detectives, solving more crimes than any other agent by the time she was 17. Then she got bored with shit and decided she needed a challenge. Potentially remembering how much the world fucked her over as a kid, she decided that challenge was fucking with the world's geography and history and created V.I.L.E.