Flowers adorn the Hollywood Walk of Fame star of a comedic icon as the world says goodbye to Joan Rivers.br br The acid-tongued comic, known for her sharp wit and classic put-downs died Thursday (September 4), a week after her heart stopped beating during an outpatient medical procedure.br br She was 81 years old.br br Her groundbreaking career paved the way for countless female comedians, like Kathy Griffin, who paid tribute to the star on Twitter, writing, "A legend, a friend, a mentor, an icon and wildly funny. One of a kind. RIP."br br Sarah Silverman tweeted "My heart is torn in half. She wasn't done."br br Rivers' can-do spirit kept her working right up until the end, on television, writing books, and performing at small comedy clubs.br br Fans of Rivers gathered outside New York's Mount Sinai hospital, where she passed away.