Ireland’s greatest mathematician, whose work in general mechanics facilitated later advances in quantum theory. He is perhaps best known in pure mathematics for his algebraic theory of complex numbers, the invention of quaternions, and the exploitation of non‐commutative algebra. A child prodigy, he could, it is claimed, speak 13 languages at the age of 13. He became Professor of Astronomy at Dublin and Royal Astronomer of Ireland at the age of 22.