<human>:  Who discovered dark matter?
<bot>: Dark matter was first postulated by Fritz Zwicky in 1933. He was a Swiss-American astronomer who studied the motion of galaxies in clusters. He concluded that the gravity of the cluster galaxies was not strong enough to hold them together. To explain this, he suggested that there was a new type of matter, which he called “dunkle Materie” or “dark matter”.