This paper aims to motivate and exemplify the use of theatre to exhibit the human drama behind mathematics-making, by communicating a sympathetic understanding of mathematicians in their historical context. (In this way, the ESU 8 talk served also as an introduction and motivation for a workshop incorporating a play about Niels Abel.) Historical processes of profound transformation in human numerical cognition are illustrated by John Wallis, speaking in the late 17th century on negative numbers, and by Carl Friedrich Gauss and Augustin-Louis Cauchy in dialogue in the 1830s on the re-naming of ‘impossible numbers’ as ‘complex numbers’. Such theatrical devices can help teachers respond to the conceptual difficulties faced by learners. By evoking the intellectual adventure through which notions like ‘irrational’, ‘fictional’, ‘false’, ‘real’, ‘imaginary’, and ‘impossible’, were negotiated, refined, named and re-named, learners may be encouraged to see negatives and complex numbers as wonderful products of a human quest.