He looms larger than life in Britain’s imagination; he’s even on the 20 pound note.

Yet as museums across the country celebrate the 250th anniversary of the birth of J.M.W. Turner — the English Romantic painter known for his images of violent sea squalls, bucolic landscapes and otherworldly sunsets — the facts of his biography are sparse and frequently contested.

Records show Turner was baptized on May 14, 1775, but the date on which he was born is unknown. He often told people it was April 23, the same as William Shakespeare. Other times, he said he shared his birth year with Napoleon and the first Duke of Wellington, both of whom were born in 1769.

In his later years, Turner adopted the title Mr. Booth, using the last name of his long-term companion, Sophia. Neighbors assumed that he was a retired officer, because of his navy greatcoat, and called him “The Admiral.”

Some say that on his deathbed in 1851, Turner’s last words were “The sun is God,” and who wouldn’t want to believe that of an artist whose medium was paint, but also light? Light through clouds, light on water, light fiery and golden through skies that blur into a vast field of color, light from flames engulfing the Houses of Parliament, light through rain, steam and speed.

“He probably didn’t tie himself to the top of a mast to be exposed to the elements,” said Amy Concannon, a senior curator at Tate Britain, which has the world’s largest Turner collection, referring to another possibly apocryphal tale about the artist. “But his claims tell us something about what he was trying to do with his art, which was not just to depict, but to express, the feeling of a scene.”