Krang's extensive backstory in the original series is explained through episodes

[Refractive Reflections]

Originally Posted by CyberCubed

12) Antrax is called, "Krang's royal executioner," which is actually pretty gruesome for old toon standards.

Do you know which episode this was in CyberCubed? ...I'm just curious because I don't remember.

Originally Posted by CyberCubed

If you actually take the time to notice all of the Krang history tidbits in the original series, there's actually a lot to piece together. This is what I love about the original cartoon, it seems simple on the surface but when you dig deep enough you find things you didn't notice before.

While I don't think the OT writers had a whole backstory from the beginning, but it is very clever how (for the most part) they were able to have these tidbits fit together seamlessly. (Though the writers weren't perfect in doing so throughout the series because of the gaping continuity hole with Baxter in "Landlord of the Flies" and "Revenge Of The Fly".) But like you said CyberCubed, it's what I like about the OT too how there are subtle clues for figuring out certain backstories for characters, grown jokes that slipped our radar as kids, and the always debatable speculation for which Turtle OT April was closest too. The OT leaves a bit mystery (which I prefer in storytelling), rather than divulging everything which evaporates the suspense and intrigue of a show.