origin of 'sad sack' (an inept blundering person)

USA, 1942, Army slang—popularised in the Army weekly ‘Yank’ by ‘The Sad Sack’, a cartoon strip by George Baker, depicting the misfortunes of an inept private

The Sad Sack During World War II ~ Vintage Everyday

The Mets Are Losers - The Atlantic

Sad Sack: The Comic Forcing Us to Think the Unthinkable, by Sewer Mutant

RIVERSIDE: George Baker created Sad Sack – Press Enterprise

George Cary Eggleston. A Rebel's Recollections

George Baker and the Sad Sack - The Comics Journal

The Era -- Day By Day, Page 400

Old Coast Guard Station

George Baker and the Sad Sack - The Comics Journal

The Sad Sack During World War II ~ Vintage Everyday

THE SAD SACK BY SGT. GEORGE BAKER 1944 HARDCOVER WWII ARMY COMIC 4th PRINTING