Yes, who can forget our old friend the Boss and his two helpers, Nuké and Mocha.  The Boss and his hilarious Boss Borot robot is the common link between the Mazinger-Grendizer series.

Of course Koji Kabuto is the main link between the series.  His Mazinger Z was what began the whole saga.  Koji then appeared at the end of the Great Mazinger series to help Great Mazinger.  Then finally we see Koji appearing in the Grendizer series.

Back to the Boss.  The Boss is someone with a lot of pride in his machine.  He certainly thinks that his Boss Borot is like non other.  The Boss sees Grendizer for the first time early in the Grendizer series.  He observes how Grendizer jumps and then connects to his Spazer saucer.

Of course, those who are familiar with the Boss know that he loves to imitate others.  So what does he do out of all things ?  Build his own Boss Spazer.

The second time the Boss appears in Grendizer was to visit his dearest friend Koji Kabuto.  At that time, Koji had no planes or anything.  So the Boss wanted to come and let Koji try out the Boss Borot with its Spazer.

Although the Boss only appeared twice in the Grendizer series, he certainly gave a nice flavour the episodes he appeared in.  In the second appearance, the Boss makes friends with Duke Freed.