Who invented the infinity symbol ∞?

The common symbol for infinity, ∞, was invented by the English mathematician John Wallis in 1655.12

Wallis introduced the symbol in his work Arithmetica Infinitorum ("The Arithmetic of Infinitesimals") to assist in his treatment of a series of squares of indivisibles. The symbol is also known as a lemniscate, a term derived from a Latin word meaning "with hanging ribbons," which reflects the shape of the curve.34