That’s one small step for (a) man, one giant leap for mankind.

Neil Armstrong (1930-2012) American astronaut, aviator, educator

Words after first stepping onto the Moon (20 Jul 1969)

The sound recording does not seem to have the "a" before man. Armstrong long insisted that he said it but it was lost in transmission; his preference has been for the "a" to be included in parentheses. Computer analysis of the recordings have yielded contradictory conclusions as to whether he said it.