I find it fascinating how what person in a film or an organization holds it all together. It is often not the top billed star but a supporting role makes the good great. I remember the old question asked of the conductor, “What is the hardest part to play in the orchestra? Second fiddle.
Here is just a start to get the conversation going.
Get Smart (TV) Edward Platte, the chief
Star Wars Alec Guinness, Obi Wan Kenobi
Andy Griffith Show Don Knotts, Barney Fife (my brother said this)
Star Trek James Doohan, Scottie
Secretaries in almost any organization.



Magnum PI— Higgins was the glue
All in the Family– Archie was supposed to be the villain, he ended up owning the show.
MASH– Harry Morgan -Col Potter
Miami Vice- Edward James Olmos- (Lt Castillo)- he made the bad acting by everyone else seem watchable.
Harry Morgan really held things together. I would add Dragnet.
I would add Edith Bunker, Jean Stapleton, to the list. I actually never found out till much later that Archie became the hero of the show.