Jason Gilbert Giambi (; born January 8, 1971) is an American former professional baseball first baseman and designated hitter. In his Major League Baseball (MLB) career, which began in 1995, he played for the Oakland Athletics, New York Yankees, Colorado Rockies and Cleveland Indians. Giambi was the American League MVP in 2000 while with the Athletics, and is a five-time All-Star who led the American League in walks four times, in on-base percentage three times, and in doubles and in slugging percentage once each, and won the Silver Slugger Award twice. Giambi has publicly apologized for using performance-enhancing drugs during his career.

Late in 2003, Giambi was named by FBI officers investigating the Bay Area Laboratory Co-operative (BALCO) as being one of the baseball players believed to have received anabolic steroids from trainer Greg Anderson.  In December 2004, the San Francisco Chronicle reported it had seen Giambi's 2003 grand jury testimony in the BALCO investigation. The newspaper said that in his testimony, Giambi admitted to using several different steroids during the off-seasons from 2001 to 2003, and injecting himself with human growth hormone during the 2003 season. In a press conference prior to the 2005 season, Giambi apologized publicly to the media and his fans, though he did not specifically state what for. The lawyer who illegally leaked the testimony later pleaded guilty, and was sentenced to 2 and a half years in prison.  Giambi apologized again on May 16, 2007, this time specifically for using steroids, and urged others in the sport to do the same. "I was wrong for using that stuff", he told USA Today. "What we should have done a long time ago was stand up--players, ownership, everybody--and said, 'We made a mistake.'" When asked why he used steroids, Giambi responded: "Maybe one day I'll talk about it, but not now." Giambi did speak with George J. Mitchell, after being forced to do so by Bud Selig. Subsequently, in December 2007, the Mitchell Report included Giambi along with his brother Jeremy Giambi, who also admitted to using steroids during his career.  The prosecution in the Barry Bonds perjury case indicated they intended to call both Jason and Jeremy Giambi to testify against Bonds in his March 2009 trial.

Were there other people besides him investigated?
Barry Bonds