An important piece of information that a lot of people get wrong: These three characters are not the "Time Skeletons", as many people erroneously think! Officially, the evil trio of Time Bokan is マージョ一味 (Mājo ichimi), which translates out to "Marjo's Gang"/"The Marjo Gang". So where does the wrong name come from?
The mecha that the crew uses each week is the タイム ガイコツ (Taimu Gaikotsu)... and Gaikotsu is Skeleton! As the crew almost always sing their song "Soreyuke Gaikotsu"("Let's Go Gaikotsu") about how evil they are every episode, it's easy for an outside observer to assume the song's name is just another "Tensei Doronbo" situation. But now you know: Marjo's Gang is the original evil trio of anime, and the Time Skeleton is the control unit of the evil trio's mecha of the week.