A background officer on Kirk's Enterprise, played by extra William Blackburn, who most often fills in at the helm or navigation console and is named on screen only once.
Lieutenant Hadley is one of the familiar silent faces of the original series bridge. He was played by William Blackburn, a regular extra who appeared in more episodes than almost any other background performer.
Hadley is usually seen as relief helmsman or navigator when Sulu or Chekov are away, but he also turns up at engineering and science stations and in security details. His name is spoken only in A Piece of the Action, when Kirk leaves instructions for the bridge.
He shares the crew's misfortunes in episodes such as Space Seed, This Side of Paradise, By Any Other Name and And the Children Shall Lead, and can be spotted from The Corbomite Maneuver through to the third season.