Almost forgotten today, the English polymath Robert Leslie Ellis (1817-1859) was lauded by his contemporaries as a ‘prodigy of universal genius’ and an ‘ideal of a University man’. Having been privately educated at Bath, reading Xenophon and Virgil and solving equations from the age of 10, Ellis went up to Trinity College, Cambridge in 1836, where he became a pupil of George Peacock and William Hopkins. A great academic career beckoned; he helped D. F. Gregory to found the Cambridge Mathematical Journal in 1837, graduated Senior Wrangler in 1840 and was elected Fellow of Trinity shortly afterwards. During the 1840s, Ellis published major papers on functional and differential equations and probability theory and took on the co-editing, with James Spedding and Douglas Denon Heath, of Francis Bacon’s Works. From 1847, Ellis’s health deteriorated and in 1849, aged 32, he returned home from a grand tour as an invalid, having been struck by rheumatic fever at San Remo. The rest of his short life was spent at Anstey Hall, Trumpington, where he saw much of his friends John Grote and William Walton, to whom he dictated his thoughts on topics ranging from etymology and bees’ cells to Roman law and a projected Chinese dictionary.