When I was younger I was deeply impressed by Douglas R. Hofstadter’s book “Gödel, Escher, Bach: An Eternal Golden Braid.” The “Gödel” in the title of that book refers to Kurt Gödel who was one of the greatest mathematicians of the 20’th century. Gödel and Einstein both worked at IAS (Institute for Advanced Study) at Princeton in the second half of their careers.
Gödel and Einstein developed a friendship at IAS. They took long walks together. According to Oskar Morgenstern Einstein said that his “own work no longer meant much, that he came to the Institute merely … to have the privilege of walking home with Gödel.”
Gödel is known for his incompleteness theorems. He published his two incompleteness theorems in 1931 when he was 25 years old, one year after finishing his doctorate at the University of Vienna. He has many other contributions to mathematics. You can also take a look at the SEP article on Kurt Gödel.
During his many years at IAS, Gödel’s interests turned to philosophy and physics. In the early 1970s, Gödel circulated among his friends an elaboration of Leibniz’s version of ontological proof of God’s existence. This is now known as Gödel’s ontological proof.
Gödel had a tragic death. He starved himself to death. Gödel had an obsessive fear of being poisoned; he would eat only food that his wife, Adele, prepared for him. Late in 1977, she was hospitalized for six months and could no longer prepare her husband’s food. In her absence, he refused to eat, eventually starving to death.