Lexell, who spent most of his career in Russia, is known for his work on cometary orbits and on spherical geometry. He arrived in St Petersburg when its eminence grise, Euler, was over 60 and practically blind. He helped Euler in his work as one of his disciples, became his friend and chosen successor, and was present when he died (Lexell himself however dying young, barely a year later). Linnaeus was one of his correspondents. Although Lexell wrote at least once to William Herschel, the discoverer of Uranus, confirming its status as a planet and calculating its orbit, the extent of any further contact is not clear.