Massachusetts Sen. William "Mo" Cowan has co-sponsored a bill seeking a posthumous presidential pardon for boxing legend John Arthur "Jack" Johnson, who was sent to prison based on a racially motivated conviction in 1913.

Cowan, a black Democrat, joined Republican Sen. John McCain of Arizona, Democratic House Majority Leader Harry Reid of Nevada and Republican Rep. Peter King of New York in asking Democratic President Barack Obama to pardon Johnson.

Johnson, the first black heavyweight boxing champion, was born in Texas in 1878. He won the title in 1908, beating boxer Tommy Burns in a match in Australia. Racial animosity was high at that time, and white boxing fans searched for a “Great White Hope” to beat Johnson. In 1910, former heavyweight champion James Jeffries came out of retirement to fight Johnson, and Johnson’s victory in the celebrated match sparked race riots around the country. Johnson would hold onto his title until 1915.

In 1913, Johnson was convicted of violating the Mann Act, which prohibited taking women across state lines for "immoral purposes." The act was meant to prevent human trafficking of prostitutes. Johnson took the white woman he was dating – and would later marry – across state lines.

After his conviction, Johnson fled the country for seven years, before returning in 1920 to serve a year in federal prison. The conviction hurt his career and his reputation.

Johnson has since become the subject of a play and film, “The Great White Hope,” as well as a documentary by filmmaker Ken Burns.

McCain and King have been introducing legislation asking for a presidential pardon of Johnson since 2004. Congress has previously passed a resolution calling for a pardon. Neither President George W. Bush nor Obama, the country’s first black president, has granted one. Obama last week announced 17 pardons.

“We can never completely right the wrong perpetrated against Jack Johnson during his lifetime, but this pardon is a small, meaningful step toward acknowledging his mistreatment before the law and celebrating his legacy of athletic greatness and historical significance,” McCain said in a statement.

Cowan said, “Jack Johnson was one of the great African-American athletes. His skill and perseverance to get back up every time he was knocked down made him a champion in the eyes of the sports world and for those who, like him, pursued their dreams despite racial intolerance.”

Cowan is Massachusetts’ second black senator. He was appointed by Gov. Deval Patrick to fill the vacancy after former Democratic Senator John Kerry became Secretary of State.