Betty White, the award-winning actress and comedian famed for her roles on The Golden Girls and The Mary Tyler Moore Show, has died at age 99, ABC News has confirmed.

Her longtime agent and friend, Jeff Witjas, told ABC News in a statement, “Betty has had a fantastic life and career and she was one of the positive people I know. I know that she is thrilled to be reunited with her [late husband] Allen Ludden.”

Best known for her television roles as Sue Ann Nivens on The Mary Tyler Moore Show and Rose Nylund on The Golden Girls, White endeared herself to audiences for decades. She told People magazine in an interview published earlier this month that one of her secrets to aging gracefully has been maintaining her sense of optimism.

“I’m so lucky to be in such good health and feel so good at this age,” she told the magazine. “It’s amazing.”

In 2013, the Guinness Book of World Records recognized White with having the longest television career for a female entertainer.

During a career that spanned more than 75 years, White received 23 Emmy nominations and won six. She also held the record as the oldest Emmy nominee overall, receiving her most recent nomination in 2012 at age 90.

Born an only child in Oak Park, Ill., Betty Marion White moved with her parents to Los Angeles at age 2. She began her career in radio, as a singer and voice actress.

Her big television break came in 1949, co-hosting a daily live variety show, Hollywood on Television. Based on one of the sketches from the show, White and two others came up with the sitcom Life with Elizabeth, in which she played the title character. The show was a huge boost for her career, and White became one of the first female producers in Hollywood.

White went on to appear in other sitcoms, late-night talk shows and daytime game shows. It was during a 1961 appearance on the game show Password that White met her third husband, the host Allen Ludden. The couple remained married for 18 years until Ludden died of stomach cancer in 1981. White never remarried. A stepmother to Ludden’s three children, White never had children of her own.

In the 1970s, White’s career got a huge boost when she was cast in The Mary Tyler Moore Show. As Sue Ann Nivens, White showed audiences a sly wit that lay behind her sweet smile. In contrast, her character on the 80s hit sitcom The Golden Girls, opposite Rue McClanahan, Bea Arthur and Estelle Getty, was, as White put it, “terminally naive.”

After The Golden Girls ended in 1992, after seven seasons, White guest-starred in a number of shows, including Ally McBeal, The Ellen Show, That ’70s Show, and Malcolm in the Middle.  Her most recent roles were playing Elka Ostrovsky in the sitcom Hot in Cleveland for six seasons, and hosting the practical jokes show Betty White’s Off Their Rockers.

Her career went through another resurgence in the mid-2000s, with White appearing in the soap opera The Bold and the Beautiful and co-starring opposite Sandra Bullock and Ryan Reynolds in the film comedy The Proposal. As her popularity continued to grow for new generations of fans, White became the oldest host of Saturday Night Live in 2010, at age 88, following a widespread Facebook campaign dubbed “Betty White to Host SNL (Please).”

Off-screen, White was an ardent advocate for animals and pets.