Sherwood Schwartz embraces actresses Florence Henderson of 'The Brady Bunch,' left, and Dawn Wells of 'Gilligan's Island' during a ceremony where he received a star on the Hollywood Walk of Fame in 2008. Associated Press

Sherwood Schwartz created "Gilligan's Island" and "The Brady Bunch," wacky television shows that drew generations of loyal viewers—and heaps of critical derision.

Mr. Schwartz, who died Tuesday at age 94, wrote and produced both shows, which have gone on to be broadcast world-wide.

Surprisingly for shows that have performed so well in syndication, neither "The Brady Bunch" nor "Gilligan's Island" was a blockbuster on first run. But audiences grew as repeats multiplied, and the shows' introductory theme songs have become cultural tropes. Each laid out the set-ups and characters—because, Mr. Schwartz told the writer Merrill Markoe, "Puzzled people cannot laugh."

Mr. Schwartz co-wrote the sea shanty, "The Ballad of Gilligan's Island."

"Both shows are pervasive," Mr. Schwartz told the Los Angeles Times in 1992. "They have left the land of television and become part of Americana."

The cast of 'The Brady Bunch' in the family living room around 1970 Getty Images

Mr. Schwartz was a veteran comedy writer who had already spent decades with Bob Hope and Red Skelton when, in 1963, he pitched CBS Chairman William Paley on the idea for a show about life after a shipwreck: A pleasure boat with five passengers and a two-man crew is grounded on an uncharted island.

But Mr. Paley was slow to embrace the concept of "Gilligan's Island," especially after Mr. Schwartz spoke of the island as a microcosm.

"A social microcosm?" Mr. Paley said. "But I thought 'Gilligan's Island' was a comedy?"

"It's a funny microcosm," Mr. Schwartz responded.

In 1995, he told Time magazine, "I knew that by assembling seven different people and forcing them to live together, the show would have great philosophical implications."

The show got its green light, but wasn't well received. "Most of TV's critics gave Sherwood's brainchild the honor of being the worst series to smell up the medium since the birth of 'The Beverly Hillbillies,' " wrote the Los Angeles Times in 1965.

For Mr. Schwartz, the miracle was that the show got made at all. "Compared to the trip of the S.S. Minnow through network waters, the maiden voyage of the Titanic was a pleasure cruise," he wrote in a memoir, "Inside Gilligan's Island."

For one thing, the shooting itself was tightly controlled by network brass, who enforced something Mr. Schwartz called "the intermittent navel rule": Dawn Wells, who played the Kansas farm girl Mary Ann, could only have her belly button on display for short times.

"Gilligan" lasted just three seasons but somehow created an outsize legacy. Mr. Schwartz's 1973 reprise of the concept, "Dusty's Trail," featured some of the same stars in leading roles but was set on a lost wagon train headed west. It folded after one season.

Alan Hale Jr. as the Skipper, left, with Bob Denver as his first mate, Gilligan Everett Collection

After "Gilligan" was canceled in 1967, Mr. Schwartz began work on "The Brady Bunch." He contended that the show was rooted in real social issues. "I realized change was occurring, that the traditional nuclear family was being replaced by other forms of marriage and relationships," Mr. Schwartz said.

The premise had a widow with three daughters marrying a widower with three similarly aged sons; plots built around adolescent traumas such as "getting braces on just before graduation or getting a pimple on your face right before a big date. That's what's important to kids and that's what they keep coming back to see."

A native of Brooklyn, Mr. Schwartz studied medicine, but fell into writing after his brother, also a comedy writer, got him a job with Bob Hope's radio show in the late 1930s.

"I was faced with a major decision—writing comedy or starving to death while I cured diseases," he told TV Guide in 2008. "I made a quick career change."

Mr. Schwartz went on to write shows for Army entertainers during World War II, and after the war became a writer on the radio version of "The Adventures of Ozzie and Harriet."

He soon moved to television and wrote for several shows, including "I Married Joan," where he worked with Jim Backus, later Mr. Howell on "Gilligan's Island." He also had a long-running gig with "The Red Skelton Hour" and also worked on "My Favorite Martian."

Not long after "The Brady Bunch" was canceled in 1974, two decades of sequels began, starting with the TV movie "Rescue From Gilligan's Island."

In partnership with his son, Lloyd Schwartz, Mr. Schwartz went on to produce television reunions for both Gilligan and the Bradys, and a pair of theater films for the latter.

Mr. Schwartz professed a certain measure of mystification at his shows' enduring popularity.

"It's fine to like the show, I guess," he said in 2000, when two made-for-TV Brady movies were broadcast. "But you'd think people would have better things to do."