Space Sentinels (1977)

 

An alien race takes three Earthling to their planet, gives them superpowers and eternal youth.  Then sends them back to Earth to help protect it from threats internal and external.  Sentinel 1 is there to guide them and provide information as well.  The Maintenance Operator, a robot that provides upkeep and repairs for S1.  It has a crush on Astrea and is generally the "comedy" relief.  The other two heroes are Hercules and Mercury.  You can guess the powers they have.  They have several adventures all over the galaxy and the Earth, even going to other dimensions and times.

This is a Filmation series that greatly benefited from the huge success of Star Wars (also 1977).  It was originally titled Young Sentinels but was changed at the last minute to the Space version.  One might say that MO was a ripoff of R2D2, but the series was in production before Star Wars was released.  MO speaks modern English, no beeps or squeaks.

Filmation cartoons got better and better, and had this series contained a bit more action (impossible in the 70s) it would have been even better.  It has good voice actors, great characters (MO is not terrible, but could be toned down a bit) and the stories are pretty good.  Hercules would later appear in the Freedom Force.