Given the nickname, "The Rocket" for a fastball clocked at times at 100 mph, Clemens became known for an intense dedication to training and conditioning that allowed him to thrive on the mound into his 40s.
Now the 48-year-old Texan faces charges related to lying to the US Congress about using performance-enhancing drugs, and if convicted on all charges could face up to 30 years in prison and a $1.5 million fine.
Clemens won an unprecedented seven Cy Young Awards as the best pitcher in his league, taking the honours for four different teams and capping his haul with the 2004 National League award, at the age of 41, with the Houston Astros.
It was success into his 40s that first aroused suspicion that Clemens used drugs. Steroids are believed to help athletes recover more quickly from injuries and enable some to maintain high levels of performance despite growing older.
The University of Texas product who pitched for the Boston Red Sox, Toronto Blue Jays, New York Yankees and the Astros, finished his 24-season career with a 354-184 lifetime mark and stands third on the all-time Major League Baseball strikeouts list with 4,672, trailing only fellow fireballers Nolan Ryan and Randy Johnson.
Clemens broke in with the Red Sox and pitched 13 seasons for Boston, leading them to the 1986 World Series with a 24-4 record that earned him American League Most Valuable Player honours and his first Cy Young.
During that campaign, Clemens became the first to strike out 20 batters in a nine-inning major league game.
Clemens won three Cy Young Awards while calling hitter-friendly Fenway Park his home, but after a few mediocre seasons towards the end of his tenure there and some injury worries he was let go by Boston and moved to Toronto.
The beefy, 6-foot-4 (1.93 metre) Clemens rebounded with a vengeance as a Blue Jay, posting back-to-back 20-win seasons in 1997 and 1998 and winning a pair of Cy Young Awards.
It was in Toronto that Clemens began working with strength and conditioning coach Brian McNamee.
TESTIMONY GIVEN UNDER OATH
The perjury charges announced Thursday stemmed from testimony Clemens and McNamee gave under oath two years ago to a House of Representatives panel that contradicted each other on whether Clemens had used banned substances.
Clemens moved from Toronto to the New York Yankees in 1999, and the big right-hander earned his first two World Series rings in his first two seasons with the Bronx Bombers. A year later, he won another Cy Young in 2001.
During the 2000 Fall Classic against cross-town rivals the New York Mets, dubbed the "Subway Series", Clemens showed his fire in a controversial incident with Mets slugger Mike Piazza.
Piazza, who had been hit in the head by a Clemens fastball earlier in the season during interleague play that gave the Mets catcher a concussion, had his bat snap in half on a swing against Clemens early in Game Two of the Series.
The ball went foul, but the barrel of the bat flew towards Clemens, who came off the mound, grabbed the splintered piece of wood and hurled it towards the baseline, nearly hitting Piazza who had started towards first base.
Clemens after the game said he did not see Piazza and threw the bat because he was pumped up with nervous energy and initially thought the fragmented bat was the ball.
In December 2007 the Mitchell Report on performance-enhancing drugs in baseball, commissioned by MLB Commissioner Bud Selig, was issued and Clemens was prominently mentioned -- one of more than 80 players cited during the so-called steroids era of the previous decade.
Clemens, who disputed his inclusion in the report, went 6-6 for the Yankees in the 2007 season before release of the report and did not pitch again.
Given the five-year waiting period from retirement to eligibility for election to the Baseball Hall of Fame in Cooperstown, New York, Clemens would not be on the ballot 2012. Candidates are voted upon by members of the Baseball Writers' Association of America.
No player who has been linked to performance-enhancing drugs has won election to the Hall, including Mark McGwire, who at one time held the single-season home run record.
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