Lou Brock, the St. Louis Cardinals' speedster who was a first-ballot member of Baseball's Hall of Fame, has died at 81, the team told ESPN.

The Cardinals and Chicago Cubs observed a moment of silence in the outfielder's memory before their game at Wrigley Field.

"Over my 25-plus years of being his agent, he was perhaps the happiest Hall of Famer I've ever encountered,'' Dick Zitzmann, Brock's longtime agent and friend, said of Brock Sunday. "I think he led a life that will never be duplicated."

Brock retired in 1979 as the single-season and all-time leader in stolen bases; marks since surpassed by Rickey Henderson. He was elected into the Hall of Fame in 1985.

After showing flashes of his potential with the Cubs, Brock's career took off when he was traded to the St. Louis Cardinals on June 15, 1964. Acquired in a trade for pitcher Ernie Broglio, Brock became the team's left fielder and hit .348 with 12 homers, 44 RBI and 33 steals in just 103 games.

The Cardinals won the World Series in seven games over the Yankees in '64 and Brock would lead the team back to the Series again in '67 and '68. Brock had 12 hits in '67 when St. Louis beat the Boston Red Sox in seven games, then had 13 hits a year later as Detroit took the title.

Those two years were part of a 12-season stretch starting in '65 in which Brock averaged 65 steals and 99 runs scored, with an average above .300 in six of those years. He hit 21 homers and stole 52 bases in '67, the first player to hit more than 20 homers with at least 50 steals in a season.

In '74, Brock surpassed Maury Wills' single-season mark with 118 stolen bases and surpassed Ty Cobb for the career mark in '77, ending with 938.

Brock's death came after Hall of Fame pitcher Tom Seaver died Monday. Brock faced Seaver 157 times in his career. That was the most plate appearances against any pitcher for Brock, who was in turn the batter Seaver faced the most number of times, according to ESPN Stats & Info research.

The El Dorado, Arkansas native ended his 19-year career with 3,023 hits, 149 homers, 900 RBI and a .293 average.

Brock was even better in postseason play, batting .391 with four homers, 16 RBI and 14 steals in 21 World Series games. He had a record-tying 13 hits in the 1968 World Series, and in Game 4 homered, tripled and doubled as the Cardinals trounced Detroit and 31-game winner Denny McLain 10-1.

Brock never played in another World Series after 1968, but remained a star for much of the last 11 years of his career.

He was so synonymous with base stealing that in 1978 he became the first major leaguer to have an award named for him while still active -- the Lou Brock Award, for the National League's leader in steals. For Brock, base stealing was an art form and a kind of warfare. He was among the first players to study films of opposing pitchers and, once on base, relied on skill and psychology.

In his 1976 memoir "Lou Brock: Stealing is My Game," he explained his success. Take a "modest lead" and "stand perfectly still." The pitcher was obligated to move, if only "to deliver the pitch." "Furthermore, he has two things on his mind: the batter and me," Brock wrote. "I have only one thing in mind -- to steal off him. The very business of disconcerting him is marvelously complex."

Brock closed out his career in 1979 by batting .304, making his sixth All-Star Game appearance and winning the Comeback Player of the Year award. The team retired his uniform number, 20, and he was inducted into the Hall of Fame in 1985 in his first year of eligibility.

The soft-spoken Brock was determined no matter the score and sometimes angered opponents and teammates by stealing even when the Cards were far ahead. He also made two damaging mistakes that helped cost St. Louis the '68 World Series.

In Game 5, with the Cards up 3-2 in the top of the fifth and leading the series 3-1, Brock doubled with one out and seemed certain to score when Julian Javier lined a single to left. But Brock never attempted to slide and left fielder Willie Horton's strong throw arrived in time for catcher Bill Freehan to tag him out.

The Tigers were among many who cited that moment as a turning point. They rallied to win 5-3 in Game 5 and take the final two in St. Louis. In Game 7, won by Detroit 4-1, Brock made another critical lapse: He was picked off first by the Tigers' Mickey Lolich after singling to lead off the sixth inning, when there was no score.

After his playing career was over, Brock worked as a florist and a commentator for ABC's "Monday Night Baseball" and was a regular for the Cards at spring training. He served as a part-time instructor while remaining an autograph favorite for fans, some of them wearing Brock-a-brellas, a hat with an umbrella top that he designed.

The Associated Press contributed to this report.