Serena Williams named Sports Illustrated's 2015 Sportsperson of the Year

She may not have won the calendar-year Grand Slam in 2015, but Monday Serena Williams added another title to her lengthy list of achievements -- Sports Illustrated's 2015 Sportsperson of the Year.

This year Williams went for another "Serena Slam," having won the 2014 U.S. Open and continued that victory streak through each of the first three major titles in 2015. She failed to put the cherry on top of her year by winning the 2015 U.S. Open for a calendar-year Grand Slam, but the magazine's cover story focused on her impressive season leading up to that point.

On the cover, Williams is lounging on a throne wearing high heels and showing off her bare, muscular legs. Sports Illustrated tweeted that the cover was the tennis player's idea, meant to portray feminism as she sees it.

The superstar posted the cover to Instagram Monday, saying she was honored to be chosen.

"For @sportsillustrated to recognize my hard work, my dedication, and my sheer determination gives me hope to continue on and do better," Williams wrote. "This is not just an accomplishment for me, but for my whole team."

Williams was chosen for her influence off the court as well as on it, Sports Illustrated wrote. She serves as a voice for many, including "everyone from 'Lean in' women to age-defying codgers to body-shamed kids to #BlackLivesMatter protesters to, yes, the voices of racial conciliation."

Some readers disagreed with the decision to give the award to Williams, only the 10th woman to win since the award was established in 1954.

Critics cited the readers' poll the magazine conducted as evidence that the award should have gone to American Pharaoh. The first horse to win the Triple Crown in 37 years won that poll in a landslide, garnering nearly half of the votes.

Others, however, said Williams had earned the award no matter what the reader poll said.