John Aloysius McKeon[1] (/məˈkiːən/; born November 23, 1930),[2][3] nicknamed "Trader Jack," is an American former Major League Baseball manager and front-office executive.

Described upon his hiring by Marlins' general manager Larry Beinfest as a "resurrection specialist,"[4] McKeon led the Marlins to a 75–49 win–loss record, a wild card berth, victories over the San Francisco Giants and Chicago Cubs in the National League divisional and championship series playoffs, and then a six-game World Series triumph over the New York Yankees.

[5] McKeon previously managed the Kansas City Royals (1973–1975), Oakland Athletics (parts of both 1977 and 1978), San Diego Padres (1988–1990), and Cincinnati Reds (1997–2000).

From July 7, 1980, through September 22, 1990, he served as the general manager of the Padres, assembling the team which won the 1984 National League pennant, the first in franchise history.

He became a playing manager in 1955 at age 24, and then worked in the farm system of the original, modern-era Washington Senators franchise, and its successor, the Minnesota Twins, handling Triple-A assignments for the Vancouver Mounties (1962), Dallas-Fort Worth Rangers (1963) and Atlanta Crackers (Opening Day through June 21, 1964).

Paced by the slugging of first baseman John Mayberry, an All-Star performance from centerfielder Amos Otis and the 20-win season of left-hander Paul Splittorff, McKeon's 1973 club finished with a record of 88 wins and 74 losses, for a .543 winning percentage; it was the best record yet compiled by the five-year-old franchise, six games behind the eventual world champion Oakland Athletics in the AL West and the fourth-best mark in the American League.

McKeon's relationship with some of the players soured late in the campaign after his demand that hitting coach Charley Lau be relieved of his duties resulted in the latter's reassignment to the minor leagues in 1975.

Two months after primary starting pitcher Steve Busby threatened to quit the team, McKeon was fired and replaced by California Angels third-base coach Whitey Herzog on July 24, 1975.

[10] Herzog led Kansas City to three successive AL West titles (1976–78), and, in the 1980s, he would become one of McKeon's trading partners when both were general managers in the National League.

At season's end, he was named to succeed Chuck Tanner as manager of the 1977 Oakland Athletics during a time when meddlesome team owner Charlie Finley was trading away veteran talent in anticipation of free agency.

Nevertheless, McKeon had led the stripped-down 1977 A's to a respectable 26–27 mark by June 8, only six games out of first place in the AL West, when Finley shocked baseball by replacing him with Bobby Winkles.

[12] McKeon then returned to the manager's post and finished the 1978 season, with Oakland winning only 45 of 123 games and falling into sixth place in the seven-team AL West.

During the 1980 All-Star break, with the Padres in last place in the National League West Division, owner Ray Kroc and club president Ballard Smith fired Fontaine and replaced him with McKeon, making him a first-time general manager at the age of 49.

Over the next four off seasons, he would also trade for Dave Dravecky, Garry Templeton, Carmelo Martínez, and Graig Nettles, draft young stars Tony Gwynn and Kevin McReynolds, and sign free agents Steve Garvey and Goose Gossage, the core of San Diego's 1984 National League champions.

Slightly more than two months later, he was ousted from the general manager's job when the Padres' new owner, Tom Werner, hired Joe McIlvaine away from the New York Mets.

McKeon was out of baseball in 1991–92 before joining the Cincinnati Reds in 1993 as a Major League scout and then senior adviser for player personnel, working under GM Jim Bowden.

He then survived a poor 1998 campaign, with Cincinnati again posting a sub-.500 (77–85) record and finishing 25 games out of first place in its division (though the Reds had lost talent from previous years and were actually considered to have overachieved).

Jack McKeon's grandson, Kellan, is a two-time state champion wrestler for Chapel Hill High School and was the captain of the wrestling team at Duke University.