Carmen Sandiego/WMG

Carmen Sandiego is a bored immortal.
That's why she is such a Friendly Enemy, she's just in it to have fun because she's got nothing else to do. She'll even help her enemies as long as she has someone to compete with. It explains her worldly knowledge, and doing stealing impossible things just because she knows she won't die doing it.

The "Player" is the true head of ACME and a child genius.
The "Player" is shown at the beginning of each episode communicating with Carmen and responding to her challenges via computer before dispatching Zack and Ivy. Assuming that everything takes place in the same universe, the "Player" is the one who is truly controlling ACME's actions, with the Chief as an AI messenger and assistant. The "Player" is in truth a boy/girl genius in the mold of L who, because of his/her young age, had limited mobility and time, Therefore, the only way he/she could solve mysteries was by providing advice online to other detectives, using them as gophers. The Chief was created to serve as a front, but also helped to monitor crime activity through the internet. No one in ACME knows of the player's identity, so it's shown that "Player" does a good job covering it up.

Ivan Idea is a Time Lord.
His cap is his TARDIS.

If Carmen and Waldo had children...
The children would be either: This is assuming they manage to locate each other for longer than five minutes... Alternatively, their child could be Ryoga
 * Completely invisible, or
 * The world's greatest spies
 * In Magical Girl Ranko vs Z Fighter Ryouga (yes, it's a crack fic, and the sequel of the infamous Ryouga vs the Road Runner), Ryoga accidentally told Ukyo that his mother is an international criminal, but then said he was joking and that his mother definitely isn't the head of an international organization named V.I.L.E.. Wisely, Ukyo decided she didn't actually want to know.
 * Phineas and Ferb could find the children, It's just they would have their memories wiped/stolen.

Carmen stole Alucard's clothes once.
She keeps wearing them since it amuses to no end to have managed to humiliate the greatest of vampires like that.

Patty Larceny's father is named Grant.
Grant Larceny

Carmen Sandiego is actually a man.
His real name is Carlos Sandiego and he is a post-op transexual who is disgusted with his new body, so he didn't pay for it and now the police are looking for him.
 * But this is THE Carmen Sandiego we're talking about! If she were conceived as a man and wanted to be a woman it would be easier, with her immense skill, to go back in time and steal her Y chromosome and replace it with another X chromosome.

Carmen Sandiego wants the player to catch her
Carmen got sick of people not respecting thier cutural heritage. Like they say, you don't know what you've got until it's gone, so she steals stuff and challenges people to catch her in order to get it back, and hopefully learn a thing or two along the way. ACME knows this, but of course stealing it not just the sort of thing you can ignore, so they all just roll thier eyes and say, "Here We Go Again..."
 * Treasures of Knowledge almost makes this canon.

In the Facebook's Carmen Sandiego's final special mission: you will be traveling in time to find Carmen Sandiego.

 * Outta of Time is the name for the final arc. Carmen kidnapped Dr. Tyhme (a pun on time) and Ivan Idea (AMCE's smart genius machinist of a kid). The reason they didn't know that Carmen put them in a trace to ask them questions about time (Dr. Thyme) and to built the machine itself (Ivan Machine.). This will be turn out a Chronoskimmer, a time machine. Though you are able to recover it -- the Chief explains even if it's a prototype, it's going to real easy for anyone to copy it and that means Carmen and her cohorts in crime have a new hobby -- time crime. This unlocks door number #2 and it's going to where the time machines crime folders are located.