Ricky Williams – the dynamic but enigmatic running back whose fascinating Dolphins career was interrupted by a stunning retirement, multiple drug suspensions and a year in the Canadian Football League – retired Tuesday, informing the Baltimore Ravens that he will not return for the second and final year of his contract.

And this time, Williams appears to be stepping aside for good.

“The NFL has been an amazing page in this chapter of my life,” Williams said in a statement. “I pray that all successive ventures offer me the same potential for growth, success, and most importantly, fun. As for what’s next, I’m excited about all the opportunities ahead – continuing my education, running the Ricky Williams Foundation, whatever opportunities present themselves.”

Williams, 34, finishes his career 26th on the NFL’s all-time rushing list (with 10,009 yards) and second in Dolphins history in that category, his 6,436 yards trailing only Larry Csonka’s 6,737.

“Thank you all, but this ain’t it,” Williams told his 83,716 followers on Twitter. “I’m going to do something really special. ‘Be you and change the world.’ ”

Williams spent seven seasons with Miami, after the Dolphins traded four draft picks – including two first-rounders – to New Orleans to acquire him.

He has the two best rushing seasons in Dolphins history: an NFL-high 1,873 in his first year in Miami (2002) and 1,372 the following season.

But Williams, faced with the prospect of missing four games because of a suspension for marijuana use, shockingly retired days before training camp in 2004. He spent the year traveling and studying at the College of Ayurveda in California and called his retirement “the most positive thing” he ever did.

He returned in 2005 to play 12 games after serving the suspension, but failed another drug test – reportedly his fourth violation– the following offseason and was suspended for all of the 2006 season, which he instead spent playing for Canadian Football League’s Toronto Argonauts.

Commissioner Roger Goodell reinstated Williams in October 2007, and then-Dolphins coach Nick Saban welcomed him back, but he suffered a season-ending pectoral injury in his first game. His next three seasons in Miami were productive and largely devoid of drama; his 1,121 rushing yards in 2009 stand fifth-most in Dolphins history.

The Dolphins did not attempt to re-sign him after the 2010 season. He signed with Baltimore, which paid him $1 million in 2011 and was due to pay him $1.5 million next season.

Williams ran for 444 yards for the Ravens, averaging 4.1 per carry, as the primary backup to Ray Rice.

“Being around him this year was the best thing that happened in my NFL career,” Rice said Tuesday. “Ricky was tremendous to learn from, the way he took care of his body, and the way he prepared – he always showed that he was a true professional. I believe Ricky Williams is a Hall of Famer.”

Ravens coach John Harbaugh said Williams “made a valuable and lasting contribution. I have the utmost respect for him.”

Williams, who finished his career with 73 touchdowns, thanked his family and several others, including two with Dolphins ties: former team executive Bill Parcells (who decided to keep Williams when Parcells joined the organization after the 2007 season) and good friend Ronnie Brown, his Dolphins teammate for five seasons.

Williams, who won the 1998 Heisman Trophy at Texas, began his NFL career in New Orleans, after Saints coach Mike Ditka traded eight draft picks, including all six of his 1999 draft choices, to Washington for the chance to select him fifth overall. He played three years with the Saints, but enjoyed his most prolific NFL seasons in the first two years with Miami.

“It was truly a blessing to play with Ricky Williams,” Dolphins cornerback Vontae Davis, who played two years with Williams, said in a tweet Tuesday. “A great person, very inspirational. Thanks for all the advice.”