It is amazing what you can accomplish if you do not care who gets the credit.

Harry S Truman (1884-1972) US President (1945-1953)

(Spurious)

There is nothing contemporary to Truman indicating this is a valid quotation of his. The earliest instance of crediting Truman seems to be by Hugh Sidey in Time (7 Nov 1988).

A variant of this quote was also attributed to Ronald Reagan, apparently due to a plaque he kept in his office:

There is no limit to what a man can do or where he can go if he does not mind who gets the credit.

More discussion of the quote and its actual origins going back to 1863: A Man May Do an Immense Deal of Good, If He Does Not Care Who Gets the Credit – Quote Investigator. See also Montague.