sad sack

noun Slang.

1. a pathetically inept person, especially a soldier, who continually blunders in spite of good intentions.

noun

1. US slang an inept person who makes mistakes despite good intentions

A singularly inept person, as in Poor George is a hopeless sad sack. This term alludes to a cartoon character, Sad Sack, invented by George Baker in 1942 and representing a soldier in ill-fitting uniform who failed at whatever he tried to do. It was soon transferred to clumsily inept civilians.