Profession: mathematician

König met his fellow-student Clairaut, as well as Maupertuis, through his studies with Johann Bernoulli (Daniel Bernoulli also taught him, as did Wolff); Clairaut became a correspondent and noted collaborator of König’s. Maupertuis introduced Voltaire and Châtelet to him, then had a famous mathematical quarrel with him, Euler putting the case against König, and Voltaire defending him in print. He travelled with his friends Voltaire and Châtelet to meet Réaumur, though Châtelet (to whom he taught algebra) later had a serious disagreement with him. Réaumur, also a friend, passed König a problem concerning the geometry of honeycombs.

Johann Bernoulli taught Euler unofficially; his friend and fellow-student Daniel Bernoulli helped persuade Euler’s father that his great gift was for mathematics, collaborated with him, and invited him to settle in St. Petersburg, where Goldbach was among his colleagues. Condorcet and Euler had an extensive working correspondence: other correspondents included Lomosonov, Clairaut, d’Alembert, Legendre, and the unreliable Stirling. Euler deputised for Maupertuis in Berlin. When Lagrange wrote to him with a new kind of calculus, he withheld his own work to let the 19-year-old get the credit. Lexell helped him when he was virtually blind.

At 19, Lagrange wrote to Euler, proposing a new form of calculus. Poisson and he spurred each other on to refine planetary mathematics. D’Alembert supported him, Laplace was a mathematical correspondent and rival, and Lavoisier intervened to ensure that Lagrange, Italian-born, would not meet hostility in post-revolutionary Paris (Lavoisier was himself beheaded a few months later). Lagrange taught Fourier and encouraged Cauchy in his studies. A paper Germain sent led her to become (as a woman and outsider) his protégée. Lambert was a close friend, and Monge visited him when he was dying.