That's right: From June 3 to July 2, there'll be a post each day highlighting Teenage Mutant Ninja Turtles canon immigrants. Now, because TMNT canon is a little confusing, it can be hard to tell what counts as a canon immigrant and what doesn't. So for the purposes of this blog, a TMNT canon immigrant is anything (a) from the movies, cartoons, video games, toy lines, or tie-in comic series that later appeared in (b) TMNT volumes 1, 2, or 4 [because they're by the original creators] or TMNT volume 5 [because the original creators are involved, it's the new official continuity, and its goal is to use as much of the diverse TMNT lore as possible].
With that in mind, let's look at today's entry: Bebop and Rocksteady!
Bebop and Rocksteady are beloved villains that first appeared in the second-ever episode of the Teenage Mutant Ninja Turtles animated series, "Enter the Shredder" (December 1987). This duo started out as two gangsters who were mutated by Shredder into a warthog and a rhino, and they became so popular that, for many people, they're as essential to the franchise as Casey Jones or even April O'Neil.
They've appeared in the toy lines, in video games, in later cartoons...basically anywhere EXCEPT the comics. They even almost appeared in the second movie until they were replaced with Tokka and Rahzar. In fact, their struggle to break into the comics is almost as if they were purposefully being kept out.
Their first-ever appearance in comics was Teenage Mutant Ninja Turtles Adventures #1 (August 1988), but it was a spin-off of the cartoon so it doesn't really count. They didn't appear in an in-continuity story until twenty years later(!) in Tales of the Teenage Mutant Ninja Turtles #58 (March 2009), but THAT was a glimpse into the multiverse.
It wasn't until IDW's Teenage Mutant Ninja Turtles Micro-Series: Raphael #1 (December 2011) that they first truly appeared in comics continuity. Their first appearance in the series proper was Teenage Mutant Ninja Turtles #25 (August 2013).
I honestly don't know why it took so long; as I said above, they're an almost necessary part of the franchise at this point, which is one of the reasons they were included in Teenage Mutant Ninja Turtles: Out of the Shadows, in theatres now!