When was the first evidence for dark matter in a galaxy cluster reported?

In 1933, astronomer Fritz Zwicky studied the Coma Cluster and found that the visible galaxies did not contain enough mass to hold the cluster together. He called the unseen component “dunkle Materie,” or dark matter. Although the idea was not widely accepted at the time, it became one of the first strong clues that most matter in the universe is invisible. Later observations of galaxy rotation and gravitational lensing strengthened the case.