The wise old professional
I don’t love to characterize Roger Sterling as “old” because he’s so dreamy and suave, but he’s the king of this trope in the modern TV era. You know this one well, too. It’s the smarter, savvier, more seasoned person in our hero’s immediate vicinity who is there to offer wisdom and guidance when they feel lost.
Even though the mentor is often wiser, smarter, and clearly more adept at everything, they can never be our hero or main lead because they aren’t the chosen one. Their role is to mold and teach, and they serve to help the protagonist stand on their own two feet.
Sometimes the mentor has to die to motivate the hero, while other times the mentor has to suffer a fall or embarrassment so that the hero can surpass them. In recent years, the TV mentor has evolved into a sexy, more distinguished version of the Old Master (think Mr. Miyagi in The Karate Kid).
The wise professional is responsible for passing on their wisdom, because they’ve probably already peaked in their professional endeavors. They are still relevant and probably far cooler than our main character. However, once the hero comes into their own, they must step aside to make way for the new up and comer, and dispense advice as needed (which is often, especially depending on the actor’s contract).
Examples: Buffy the Vampire Slayer, Mad Men, Game of Thrones, and Supernatural