Business person who specializes in drilling. Companies who wish wells drilled call for bids to drill well(s) to certain depths and other specifics. A good record as a responsible, competent contractor will help win bids.
Hired by the drilling contractor to supervise a drilling rig and its crews. Since the rig operates 24 hours a day, seven days a week, this usually means supervising three crews, supervising the drilling operation, and working with the contractor. While the rig is operating, the "toolpush" is always on call.
The driller is directly responsible for the drilling of the hole: supervising the rig crew, controlling what happens on the rig floor, and running the controls which drill the well.
When the pipe must be taken out (tripping out) to change bits or for other reasons, the derrickhand handles the top end of the pipe rack. Working on the "monkey board" high overhead, the derrickhand helps stack the pipe and then when the pipe is tripped in, guides the top end of each pipe as it is rejoined to the drill string. In between trips, the derrickhand usually operates the mud system, making sure it is meeting the specifications for drilling a particular part of the hole.
Usually two per drilling crew, the roughnecks handle the lower end of the pipe when it is tripping out or in. They also attach each length of new drill pipe as it is needed as the well gets deeper. This is heavy, exacting work and requires precise timing and teamwork. Roughnecks also maintain and repair the rig, and other equipment, and keep the rig floor a safe operating area.