What villains have been in every iteration?
 

There's Baxter and Shredder in the comics and every other cartoon. (Not counting movies) and Karai even though she wasn't in OT. Who are the true main villains and ones that have been in every iteration (comics, and tv shows) you can even exclude the new show cause its still pretty green, and some of you may not count it as part of the franchise which is understandable. You can Also exclude The Next mutation, it's live action, was a tv show but wasn't one of the cartoons and did it's own thing so you can't really count it.

The Rat King

(was going to say Slash too but he wasn't in 2K3 :ohwell:)

Oh boy are you gonna get a lot of hate for that last sentance. Who was always there? Rat king? No, no he wasn't in the movies, or idw. This is a tough one...
Shredder is the only one who consistently shows up everywhere...

Only Shredder has been because he's the only villain that wasn't original in The Next Mutation. Or what we are also not going to count TNM? Well you ask what villains have been in ever iteration and then make exceptions in the OP. Maybe the thread should be renamed "What villains have appeared in the most iterations?" in that case, if not then we know the answer and that's Shredder.

Every iteration?

I'm pretty sure Shredder wasn't in the Superhero canon, where Splinter, named Sliver is the main villain. Well, the is a guy named Shreddarius, but he have little in common with Oroku Saki/Shredder. Except being a bad guy of course.

Here's the full list of characters to appear in every major TMNT incarnation:

Michelangelo
Donatello
Raphael
Leonardo
Splinter
Oroku Saki

That's it.

Taking The Next Mutation out only adds April.

Taking the movies out adds Baxter, Leatherhead and the Rat King (provided you don't count the Fred Wolf-inspired anime and manga offshoots as their own things).

The guys excluded the movies :P

Excluding the movies:

Shredder, the Foot, Baxter, Mousers, Rat King, and Leatherhead.

Now it seems like Karai will also be in every incarnation.