Maupertuis was taught by Bernoulli, who encouraged his development of Newton’s theories; König was a fellow-student, though a famous and bitter mathematical quarrel marked their last years. Marivaux was a friend as a young man in Paris. Maupertuis was Châtelet’s geometry tutor and lover, and also taught Buffon. Clairaut accompanied him on a year-long expedition to Lapland (they met Celsius en route), though the friendship eventually deteriorated. His great friend Euler wrote to him for two decades, and deputised for him in Berlin. Voltaire had been a good friend, but mocked his ideas and his relations with Lapp women.