Given the amount of machismo sports we follow in the United States—football, basketball, wrestling—tennis sometimes doesn't get its proper due. There's no physical contact, no wild crashes, and no gruseome injuries—it's popularily viewed alongside golf as a leisure sport. That shouldn't, however, prevent us from acknowledging the true American badasses who have taken the court. From Serena Williams' fire and Andre Agassi's career-saving lifestyle changes to Billie Jean King's championships and social activism, these are the Most Badass Americans in Tennis History.

*We've included a couple naturalized citizens for this list.*

RELATED: 20 Things You Didn't Know About the U.S. Open