After years as a respected power hitter, Sammy Sosa emerged during the 1998 season as one of baseball's greats. It was in this season that both Sosa and Mark McGwire broke Roger Maris's long-standing single season home run record of 61. Sosa ended the season with 66, behind McGwire's 70. His 416 total bases were the most in a single season in 50 years, since Stan Musial's 429 in 1948. Sosa found some consolation in winning the National League Most Valuable Player Award for 1998, earning every first-place vote except for the two cast by St. Louis writers, who voted for McGwire.
In 2001, he hit 64 home runs, becoming the first (and, thus far, only) player ever with three 60 home run seasons (though, oddly, he did not lead the league in any of those three seasons; in 2001, he finished behind Barry Bonds). In the same season he set personal records in runs scored (146), RBIs (160), walks (116), on base percentage (.437), slugging percentage (.737), and batting average (.328). He led the Majors in runs and RBIs, was 2nd in home runs, 2nd in slugging percentage, 3rd in walks, 4th in on base percentage, 12th in batting average, and 15th in hits. He also surpassed his 1998 numbers in total bases, compiling 425.
Sosa was born in San Pedro de Macoris, Dominican Republic, where he grew up in an abandoned hospital. He originally signed with the Philadelphia Phillies at age 15, but this deal was not allowed by Major League Baseball because of Sosa's age. He signed with the Texas Rangers in 1985.
Sosa began his Major League career in 1989 with the Rangers. After being sent again to the minors, he was traded to the Chicago White Sox (a move that U.S. President George W. Bush, then the Rangers' owner, later joked was the biggest mistake he ever made). After nearly two years with the White Sox, he was again sent down to the minors midseason 1991. Recalled late in the season, he failed to impress the White Sox management, who dealt him away to the Chicago Cubs just prior to the 1992 season. It was there that Sosa spent his glory years.
Known as a free-swinger in his early years, and as an easy strikeout candidate, Sosa has become an effective hitter for average. He owns numerous team records for the Cubs, and holds the major-league record for the most home runs hit in a month (20, in June 1998).
On June 3, 2003, Sosa was ejected from a Cubs-Devil Rays game in the first inning when umpires discovered he had been using a corked bat.  Major League Baseball confiscated 76 of Sosa's other bats after his ejection, and all were found to be clean, with no cork.  Sosa stated that he had accidentally used the corked bat. On June 6, 2003, Sosa was suspended for eight games on account of the corked bat.  However, the suspension was reduced by one game on June 11, 2003. 
Since the suspension, Sosa has been on a tear and has regained the form that marked his four consecutive 50 home run seasons.