Complex numbers were first used in the 16th century in order to solve cubic equations, as there are some cases with real solutions that nonetheless require the use of complex numbers in order to obtain those solutions. The recognition of the complex numbers as an object worthy of study in their own right is usually attributed to Rafael Bombelli, who in 1572 was the first to formalize the rules of complex arithmetic (and also, at the same time, the first to write down the rules for manipulating negative numbers!) The term imaginary was introduced only later, by René Descartes in 1637.