Sy Berger’s card was part of the 2004 Topps series called All-Time Fan Favorites.

Sy Berger, a chewing gum executive who helped turn the humble baseball card, an item collected and bartered by boys, into a pop-culture phenomenon that is sometimes sold at auction for as much as seven figures, died Dec. 14 at his home in Rockville Centre, N.Y. He was 91.

His wife, Gloria Berger, said he suffered respiratory distress at home after having been released from a hospital for treatment of pneumonia.

In the late 19th century, baseball cards made their first appearance on the American scene, often as an adjunct to tobacco products.

Through the Depression of the 1930s, they were a gimmick to boost sales of certain products. But it was in the post-World War II era that baseball cards came into their own, and it was in that era that Mr. Berger launched his career.

As an executive of the Brooklyn-based Topps Co., Mr. Berger created the basic design of the color portraits of major league ballplayers, which then were imprinted on playing-card-sized pieces of cardboard and sold with packages of gum.

Across the United States, they were collected and traded by millions of youngsters. Some could fetch more in a trade than others.

A Yogi Berra card, for example, was worth more than one of his 1955 New York Yankee teammates Hank Bauer or Marv Throneberry. And location mattered. A Roy Campanella card would bring more in Brooklyn in 1955 than you could reasonably expect to get in the Bronx for the Dodger catcher.

Most self-respecting 12-year-olds could increase their baseball card collections in honest competition. From an equal distance, contestants pitched their card against a wall, holding it between the middle and index finger, and tossing it a backhand, sidearm motion, like a Frisbee.

The pitcher of the card landing closest to the wall collected all the other cards in the contest. This game was almost always “played for keeps.”

In 2004, Mr. Berger told the Society for American Baseball Research that “value appreciation” was the greatest change that had taken place in his industry because of the skyrocketing worth of many of the old cards.

“Mama used to give you a nickel and say, ‘Now don’t buy those stupid baseball cards,’ ” he told the society. “And now she’s saying, ‘And remember, don’t forget to buy the baseball cards so you can go to college!’ ”

Seymour Perry Berger was born in New York City on July 12, 1923, and he collected baseball cards in childhood. He enrolled at Bucknell University in Lewisburg, Pa., with the class of 1944 but did not graduate until 1946, following service in the Army Air Forces during World War II.

Survivors include his wife of 69 years, Gloria Karpf Berger of Rockville Centre; three children, Glenn Berger of Concord, N.H., Maxine Berger Bienstock of New York City and Gary Berger of Glen Cove, N.Y.; five grandchildren; and two great-grandchildren.

Mr. Berger joined Topps in 1947 and in 1951 turned his attention to baseball cards, which until that point had consisted of little more than a gray and white photograph of a ballplayer superimposed on cardboard. Mr. Berger added color, a facsimile of the player’s autograph and statistics.

The joy of his job, Mr. Berger often said, was meeting and socializing with the players while getting their authorization for Topps to use their names and pictures on its baseball cards.

During his early years with the company, the three New York teams — the Yankees, Giants and Dodgers — dominated major league baseball, and Mr. Berger was given clubhouse access to the players.

“Willie Mays, of course had a great impact,” he told the Society for American Baseball Research. “I am still his oldest and best friend, and I handle most of his business affairs now. . . . So I was known as Willie’s friend.”

Knowing the future Hall of Famer gave Mr. Berger entry to other players. He told the baseball research group that the athletes would say, “Well you know, if it’s good enough for Willie it’s good enough for me.”

Over the years, Mr. Berger would sign thousands of ballplayers to one-, two- and three- year contracts for usage of their names and pictures on Topps baseball cards, generally for $100 to $125 a year. He retired from Topps in 1997, then was a consultant to the company for five years.

Like most cultural phenomena, baseball cards have experienced rises and falls in popularity in the period since Mr. Berger began his career.

There was a spectacular baseball card bubble in the 1980s and 1990s when it became a billion-dollar industry, with an estimated 81 billion cards produced a year, author Dave Jamieson wrote in a 2010 book, “Mint Condition.”

Many, but not all, of these cards wound up in shoe boxes, tucked away in attics or backs of closets, only to be retrieved decades later by the aging mothers of the once-young collectors, long since flown from their boyhood nests. A few cards got back to their original owners, but more found their permanent resting places in city dumps.

A few hit the collectors’ jackpot.

According to a Bloomberg News article earlier this month, a recently discovered 1909 Honus Wagner card, featuring the Hall of Fame Pittsburgh Pirates shortstop, sold for $403,664 at an online auction. A 1952 Topps Mickey Mantle rookie card sold for $268,664.

In April 2013 a Wagner card sold for $2.1 million, a record for a public auction sale of a baseball card, according to Bloomberg.

In 1988, Mr. Berger was honored by the National Baseball Hall of Fame in Cooperstown, N.Y., for his role “in the development of the modern baseball trading card and for helping to introduce generations of fans to baseball for more than half of a century.” He also earned his own card, part of the 2004 Topps series called All-Time Fan Favorites.

Mr. Berger was not a baseball card collector himself, his wife said, preferring to call himself “a gatherer.” He did go to ballgames. There was a time when Ted Williams played for the Boston Red Sox that Mr. Berger was a Red Sox fan, his wife said. But in the later years of his life, “he was a Yankee fan.”