keyman

noun3

1. •
   An employee of vital importance to a business.

   • A corporation may feel the need for life insurance on one of its keymen under a variety of circumstances. — 1957
2. •
   (India) A workman who checks a railway track for faults, and who carries a keying hammer.
3. •
   (old-fashioned) A telegraph operator.

   • Conscious of their importance, the 324 labor delegates marched bravely in and elected by acclaim as their president a onetime Ontario telegraph keyman, Senator Gideon Decker Robertson […] — 1932