Bill Cosby's solemn tweet to mark his 75th birthday

Bill Cosby in concert at the Royal Albert Hall in London.
Bill Cosby has been entertaining crowds for generations. Photo: Simon Meaker/EMPICS Entertainment

American comedy legend Bill Cosby has celebrated his 75th birthday today.

The cantankerous star of 1980s hit The Cosby Show launched his career two decades earlier as a stand-up comic.

Bill Cosby and the cast of his hit show
Bill Cosby with the cast of his eponymous hit show. Credit: Reuters/Fred Prouser

He was soon a television trailblazer as he broke down racial barriers to earn a starring role on US prime time in I Spy.

Cosby has gone on to spread his talents as an author and leading campaigner on social and educational issues.

Bill Cosby holding the Bob Hope Humanitarian Award
The 75-year-old has been honoured beyond comedy for his humanitarian work. Credit: PA

But his life was hit with tragedy when his only son Ennis was murdered in Los Angeles in 1997.

Responding to his new landmark age today, Cosby tweeted: