50. One to screw in the light bulb and the remaining 49 to guard him .
or
1,000,001: One to change the bulb and 1,000,000 to rebuild civilization to the point where they need light bulbs again.
or
The batter.
or
Two. One to hold the bulb and the other to rotate the planet.
or
Five. One to screw it in and four to tell him how bitchin' he looked doing it.
or