James Howard Thome (/ˈtoʊmi/; TOH-mee; born August 27, 1970) is an American former professional baseball player—a first baseman, third baseman and designated hitter—who played in Major League Baseball (MLB) for 22 seasons (1991–2012). A prolific power hitter, Thome hit 612 home runs during his career—the eighth-most all time. He amassed a total of 2,328 hits and 1,699 runs batted in (RBIs). His career batting average was .276. He was a member of five All-Star teams and won a Silver Slugger Award in 1996.

Thome grew up in Peoria, Illinois, as part of a large blue-collar family of athletes. After attending Illinois Central College, he was drafted by the Indians in the 1989 draft, and made his big league debut in 1991. With the Indians, he was part of a core of players that led the franchise to five consecutive playoff appearances in the 1990s, including World Series appearances in 1995 and 1997. Thome spent over a decade with Cleveland, before leaving via free agency after the 2002 season, to join the Philadelphia Phillies, with whom he spent the following three seasons. Traded to the Chicago White Sox before the 2006 season, he won the American League (AL) Comeback Player of the Year Award that year and joined the 500 home run club during his three-season tenure with the White Sox. By this point in his career, back pain limited Thome to being a designated hitter. After stints with the Los Angeles Dodgers and Minnesota Twins, he made brief returns to Cleveland and Philadelphia, before ending his career with the Baltimore Orioles. Upon retiring, Thome accepted an executive position with the White Sox.

Throughout his career, Thome's strength was power hitting. In 12 different seasons, he hit at least 30 home runs, topping 40 home runs in six of those seasons. He hit a career-high 52 home runs in 2002, and in 2003 he led the National League in home runs with 47. Due in part to his ability to draw walks, with 12 seasons of at least 90 bases on balls, he finished his career with a .402 on-base percentage. Thome's career on-base plus slugging (OPS) of .956 ranks 19th all-time. In 2011, he became only the eighth MLB player to hit 600 home runs. Thome is the career leader in walk-off home runs with 13. One of his trademarks was his unique batting stance, in which he held the bat out with his right hand and pointed it at right field before the pitcher threw, something he first saw in The Natural. Thome was known for his consistently positive attitude and "gregarious" personality. An active philanthropist during his playing career, he was honored with two Marvin Miller Man of the Year Awards, a Lou Gehrig Memorial Award, and a Roberto Clemente Award for his community involvement. In 2018, Thome was inducted into the National Baseball Hall of Fame in his first year of eligibility.

Thome was born in Peoria, Illinois, on August 27, 1970, and is the youngest of five children. Many of the Thome family played sports: Jim's grandmother was hired at a local Caterpillar plant solely to play for the company's softball team; his father built bulldozers for Caterpillar and played slow-pitch softball; his aunt Caroline Thome Hart is in the Women's Softball Hall of Fame; and his two older brothers, Chuck III and Randy, played baseball at Limestone High School. Thome learned to play baseball from his father on a tennis court, and also played basketball in what he described as the "ghetto" of Peoria, noting that he was the only white kid there but that he earned the respect of his fellow players. One day during his youth, Thome sneaked into the Cubs' clubhouse at Wrigley Field in an unsuccessful attempt to obtain an autograph from his favorite player, Dave Kingman. Though Thome received signatures from several other players, this experience influenced him to be generous with signing autographs for fans during his playing career.

As with his older brothers, Thome attended Limestone High School where he achieved all-state honors in basketball and as a baseball shortstop. He played American Legion Baseball for Bartonville Limestone Post 979 in his hometown, as well. Although he had hoped to draw the attention of scouts, at just 175 pounds (79 kg) he was relatively underweight for his 6-foot-2-inch (188 cm) height, meaning that he attracted only passing interest—the average Major League Baseball (MLB) player weighed 195 pounds (88 kg) in 1993. Thome graduated in 1988 and, after not being drafted, enrolled at Illinois Central College where he continued his baseball and basketball careers. After one season, he was drafted by MLB's Cleveland Indians as an "afterthought" in the 13th round (333rd overall) of the 1989 MLB draft.

For the 1989 season, Thome was assigned to the Gulf Coast League Indians, a minor league affiliate of the Cleveland Indians. He finished the year with a .237 batting average, no home runs, and 22 runs batted in (RBIs) in 55 games. After his rookie season, he met "hitting guru" Charlie Manuel, who later became his manager and mentor. Unlike most Indians staff, Manuel saw potential in Thome and worked hard with him, particularly on his hip motion while swinging the bat. Thome later said, "[Manuel] saw something in me I didn't." During this work, Manuel suggested to Thome that he point his bat out to center field before the pitch to relax himself like Roy Hobbs did when batting in the baseball film The Natural. The work paid off; in 1990, Thome hit .340 and totaled 16 home runs and 50 RBIs in 67 games playing at both the Rookie and Class A levels of the minor leagues. Thome spent most of the 1991 season splitting time between Double-A and Triple-A where, in combination, he hit .319 with seven home runs and 73 RBIs in 125 games.

Thome made his MLB debut on September 4, 1991, as a third baseman against the Minnesota Twins. In the game, he recorded two hits in four at bats (2-for-4). He hit his first career home run on October 4. Injuries shortened his 1992 campaign, during which he played for both the Indians and their Triple-A affiliate, the Colorado Springs Sky Sox. Across the minor and major leagues that year, he combined to hit .236 with four home runs and 26 RBIs in 52 games. In 1993, playing mostly for the Charlotte Knights, the Indians' new Triple-A affiliate, he led the International League with a .332 batting average and 102 RBIs, complemented by 25 home runs in 115 games. This performance earned him a late season promotion to the major league, where he hit .266 with seven home runs and 22 RBIs in 47 games.

Thome spent the entire 1994 season with Cleveland, playing in 98 games while hitting .268 with 20 home runs and 52 RBIs, before the 1994 players' strike forced cancellation of the season's remaining games. Thome achieved his first career multi-home run game, hitting two solo home runs on June 22, 1994, against Detroit Tigers' pitcher John Doherty.