Shaquille O'Neal, one of the most dominating big men in NBA history in his prime, announced his retirement Wednesday after a 19-year career that saw him win four NBA titles. "Shaq" was at his finest from 2000 through 2002 when he combined with star guard Kobe Bryant to guide the Los Angeles Lakers to three NBA crowns, and he added another in 2006 with Miami, two years after being traded to the Heat. "im retiring," O'Neal posted on his Twitter microblogging website, which also included a video link in which he thanked his followers on the social media site. O'Neal, 39, was nagged by injuries in the later seasons of his career, including failed stints to help bring titles to Phoenix, Cleveland and this season in Boston. A nagging right Achilles tendon injury proved more than "Shaq" could overcome and he told an ESPN reporter who is working on a biography of him that he considered making a comeback but did not want to disappoint Celtics fans. "I really thought about coming back but this Achilles is very damaged and if I had it done the recovery would be so long we'd have the same outcome as this last year -- everyone sitting around and waiting for me," O'Neal said. "I didn't want to let people down two years in a row. I didn't want to hold Boston hostage again. "I'm letting everybody know now so ... the organization can try to get younger talent. I would love to come back, but they say once the Achilles is damaged it's never the same. I don't want to take that chance." LeBron James, the current Miami star who played alongside O'Neal in Cleveland, appreciated "Shaq" on and off the court. "What a career for Shaq Diesel!!" James posted on his Twitter site. "The most dominating force to ever play the game. Great person to be around as well. Comedy all the time!!" Heat president Pat Riley, who coached O'Neal to an NBA title in Miami, saw the personable center's goodbye as a bittersweet moment. "I'm a little bit sad," Riley said. "Great, great player. The league is going to miss Shaq. I'm sure Shaq will do something big and beyond." O'Neal, a 15-time NBA All-Star, ranks fifth on the all-time NBA scoring list with 28,596 points and his three NBA Finals Most Valuable Player Awards trail only Michael Jordan on the all-time list. O'Neal, who ranks 12th on the NBA all-time rebound list with 13,099, played only 37 games for the Celtics this season, only three of those appearances coming in the last 2 1/2 months of the season. Among NBA players with at least 2,000 baskets, O'Neal ranks second in shooting percentage with a 58.2 percent accuracy rate. "Shaq" made the most of outside opportunities his NBA career offered, playing a genie in the 1996 movie "Kazaam" and the 1994 film "Blue Chips" where he played a young basketball star. O'Neal also made rap albums, notably talking about growing up with his mother and stepfather in the song "Biological Didn't Bother". The Orlando Magic made O'Neal the fist pick in the 1992 NBA Draft and "Shaq" was the NBA's 1993 Rookie of the Year. He won the NBA scoring title in 1995 when he helped Orlando reach the NBA Finals, only to be swept by Houston, and in 2000, when the Lakers beat Indiana for O'Neal's first NBA title. O'Neal famously announced his joining the Los Angeles Lakers in 1996 at the Atlanta Olympics, where he was a member of the US Olympic "Dream Team III" that captured a gold medal. Bryant and O'Neal grew into a formidable combination but the two grew apart and after the Lakers lost the 2004 finals to Detroit, O'Neal was traded to Miami, where he and Dwyane Wade proved a formidable pairing, bringing a title to the Heat five years ago. That was the last glory day for O'Neal, whose penchant for nicknames such as "The Big Aristotle" led him to dub himself "The Big Shaqtus" in Phoenix and "The Big Shamrock" in Boston. His final season was his worst after losing a week in November to a bruised right knee, a week in December to a calf injury and a week in January with a sore right hip before the Achilles problems. He averaged only 9.2 points and 4.8 rebounds in 37 games. O'Neal sported a Superman logo tattoo on one arm and another that featured a giant hand looming behind the Earth with the abbrevation TWISM, which stood for "The World Is Mine".