Mauldin died at a nursing home of complications from Alzheimer's disease, including pneumonia, said Andy Mauldin, one of his seven sons.
"It's really good that he's not suffering anymore," he said. "He had a terrible struggle."
Mauldin was one of the pre-eminent editorial cartoonists of the 20th century, writing and drawing 16 books.
It was at the Chicago Sun-Times where Mauldin drew one of his most famous cartoons, published after President Kennedy's assassination. It showed a grieving Abraham Lincoln, his hands covering his face, at the Lincoln Memorial.
With Willie and Joe, Mauldin became the voice of the World War II infantryman. From 1940 to 1945, the laconic pair of unshaven, slump-shouldered soldiers slogged their way through battle-scarred Europe, surviving the enemy and the elements while sarcastically mocking everything from their orders to their equipment and even their allies.
In one drawing, soldiers are marching, bone-weary. Says Willie: "Maybe Joe needs a rest. He's talking in his sleep."
In another, the two are about to jump a down-in-the-mouth German soldier walking by with a bottle of liquor. Willie says: "Don't startle 'em, Joe. It's almost full." And in another, Willie tells a medic: "Just gimme a coupla aspirin. I already got a Purple Heart."
In yet another drawing, Willie grabs a weary GI by the collar and holds up a letter from home: "My son. Five days old. Good-lookin' kid, ain't he?"
The cartoons, published in Stars and Stripes and other military journals, delighted his fellow soldiers and endeared Mauldin to Americans at home.
"I wish we had more like him," syndicated columnist Paul Conrad, who served in the Pacific during WWII. "He would have been a lot of fun to go through the war with."
In his book "Up Front," Mauldin said the expressions on Joe and Willie are "those of infantry soldiers who have been in the war for a couple of years."
"If he is looking very weary and resigned to the fact that he is probably going to die before it is over, and if he has a deep, almost hopeless desire to go home and forget it all; if he looks with dull, uncomprehending eyes at the fresh-faced kid who is talking about all the joys of battle and killing Germans, then he comes from the same infantry as Joe and Willie," Mauldin wrote.
Mauldin called himself "as independent as a hog on ice," and his nonconformist approach brought him a face-to-face upbraiding from Gen. George Patton. Mauldin continued to draw what he wanted.
In 1945, at age 23, his series "Up Front With Mauldin," featuring Willie and Joe, won him the first of his two Pulitzers for editorial cartooning.
The second prize came in 1959, while he was at the St. Louis Post-Dispatch, for depicting Soviet novelist Boris Pasternak saying to another gulag prisoner: "I won the Nobel Prize for literature. What was your crime?"
William Mauldin was born Oct. 29, 1921, near Santa Fe, N.M., and spent much of his life in the West. He attended the Academy of Fine Art in Chicago, learning from such teachers as cartoonist Vaughn Shoemaker, a Pulitzer-winner for the Chicago Daily News.
Mauldin enlisted in 1940 and, assigned as a rifleman to the 180th Infantry, started drawing cartoons depicting training camp for the Division News, the newspaper for the 45th Division.
Once Mauldin's 45th Division shipped overseas, Stars and Stripes, the military-wide newspaper, began publishing his drawings. He was later assigned to Stars and Stripes but continued to spend most of his time with the 45th Division, where he said he received his inspiration.
Author and former Vietnam War correspondent David Halberstam wrote: "One senses that if a war reporter who had been with Hannibal or Napoleon saw Mauldin's work, he would know immediately that the work was right."
After the war, Mauldin freelanced for a time. He joined the Post-Dispatch in 1958, then switched to the Sun-Times in 1962.
He also acted in two movies, including John Huston's 1951 production of "The Red Badge of Courage."
In recent years, as Mauldin battled Alzheimer's, thousands of veterans, widows and other well-wishers sent him letters, offering thanks and stories of survival.
"You have managed to capture the irony, double standards and outright insanity of Army life," one man wrote, "in a way that allows us to laugh at ourselves and our leaders and keep moving forward in the face of adversity."
The campaign to recognize him was sparked by veteran Jay Gruenfeld, who spent years wondering what happened to the man who had made him laugh in a foxhole under fire. He sought out Mauldin and then wrote to veterans organizations and contacted newspaper columnists urging people to remember him. Soon Mauldin was receiving hundreds of letters a day.
Said Andy Mauldin: "They tried to pay him back for support he had given them."
Mauldin is survived by former wives Jean Mauldin and Christine Lund and all of his sons. Funeral arrangements were incomplete, but burial is planned in Arlington National Cemetery.