Harold Humphrey Hackett (July 12, 1878 – November 20, 1937) was an American tennis player.

Born in Hingham, Massachusetts, but a long-time resident of New York, Hackett turned in his best results in doubles with Fred Alexander.

[2][3] A graduate of Yale University, Hackett and Princeton University graduate Alexander won the U.S. Indoor doubles three times (1906–08), and he teamed with Walter Hall to win the U.S. Clay Court doubles title in 1912.

[5] In 1911, Hackett's wife divorced him for alleged acts of cruelty and that he publicly accused her of having a dozen affairs.

Hackett arrived the following morning and only wanted to discuss their expense accounts, then quickly departed two hours later -- not to be heard from again for several months.