"‘a pin passed through the end of an axle to keep a wheel in position’
‘a person or thing vital to an enterprise or organization’"

Linchpin - Oxford definition
For many, the origin of this word often conjures up sedate images of country life, but whether it was the romantic notion of the collection of hay on a sunny summer afternoon, or the more frenetic environment of a charioteer in the midst of a battlefield in bygone times, the loss or breakdown of a linchpin was certainly going to spoil your day, or worse. It’s easy to see over time why the word was adopted to describe essential individuals within families or organisations.

'The modern manager has a unique skillset'
'Great managers create great teams'