Imaginary numbers were initially discovered and worked with by the Italian mathematician Gerolamo Cardano in the 16th century. Cardano encountered the need for these numbers while solving cubic equations, where he dealt with square roots of negative numbers, though he did not fully understand or utilize them and considered them somewhat useless. Later, in 1572, Rafael Bombelli provided the first proper set of rules for manipulating these "imaginary" numbers, making a crucial contribution to their development. The term "imaginary" was coined in the 17th century by René Descartes, initially as a derogatory label, but the concept gained wide acceptance following foundational work by Leonhard Euler and Carl Friedrich Gauss in the 18th and 19th centuries. Euler introduced the notation "i" for the square root of -1 and developed much of the modern theory surrounding complex numbers, while Gauss worked on their geometric interpretation in the complex plane.