President Barack Obama has pardoned a Marietta man who was convicted of heroin charges in Puerto Rico 16 years ago.

William Ricardo Alvarez was among 21 people shown clemency by Obama on Thursday, as he granted 13 pardons and commuted eight prison sentences. One of the sentences he commuted was for Helen Alexander Gray, of Ty Ty, in Tift County.

Obama has pardoned and commuted sentences at a lower rate than almost any president, but Thursday’s announcement was aimed at showing off his efforts to combat disparities in drug sentences.

Alvarez, according to the White House, was sentenced to nine months in prison and four years of supervised release in 1997 for conspiracy to possess with intent to distribute heroin and conspiracy to import heroin.

Following a five-year waiting period, people convicted of a federal crime can apply for a presidential pardon, though the odds are long.

Gray was sentenced to 20 years for cocaine possession with intent to distribute and possession of a firearm by a convicted felon. Gray is now scheduled for release in 2014 instead of 2016.

In some of the cases that Obama is commuting, judges had chafed at the mandatory minimum requirements for sentencing, he said in a statement.

“Commuting the sentences of these eight Americans is an important step toward restoring fundamental ideals of justice and fairness,” Obama said.

“But it must not be the last. In the new year, lawmakers should act on the kinds of bipartisan sentencing reform measures already working their way through Congress. Together, we must ensure that our taxpayer dollars are spent wisely, and that our justice system keeps its basic promise of equal treatment for all.”

The American Civil Liberties Union chided Obama for his low rate of pardons – in five years he had pardoned 39 people and commuted one sentence before Thursday – while praising the step to commute sentences of three people who were serving life in prison for nonviolent offenses.

“We hope the president will continue to exercise his clemency powers and lend his support to systemic reform that will make our criminal justice system smarter, fairer and more humane,” said Vanita Gupta, deputy legal director of ACLU.

Christian Boone contributed to this report.