keyman

Noun

 * 1)  A telegraph operator.
 * 2) * 1932, Time (volume 19, part 2)
 * 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
 * 1)  A workman who checks a railway track for faults, and who carries a keying hammer.
 * 2) An employee of vital importance to a business.