Based on a True Story

Everything About Fiction You Never Wanted to Know.
And it's all true.
—Theatrical release posters for Dog Day Afternoon.

A Stock Phrase in fictional works of all kinds. Popular, partly because you can get away with more outrageous elements if you say "The Tasteless But True Story", and partly because some works happen to be based on true stories.

Strength of Basis

As an illustrative example, we will use the story of Donald Sheer finding an original copy of the Declaration of Independence behind a painting bought at a flea market and auctioning it for US$2.42 million.

Related Tropes

No examples, please; add them to the subtropes instead.