Large-scale structure of the Universe
Dark Matter's existence was first postulated by Swiss astronomer Fritz Zwicky who hypothesized it's existence based on observations of the Coma Cluster. Applying the virial theorem, Zwicky noticed that there was an apparent contradiction based on the speed of the galaxies which indirectly led him to obtain evidence of dark matter which he called dunkle materie (literally dark matter). Zwicky estimated its mass based on the motions of galaxies near its edge and compared that to an estimate based on its brightness and number of galaxies. He estimated the cluster had about 400 times more mass than was visually observable. The gravitational effect of the visible galaxies was far too small for such fast orbits, thus there must have been mass hidden from view. Based on these conclusions, Zwicky inferred that some unseen matter provided the mass and associated gravitational attraction to hold the cluster together. Zwicky's estimates were off by more than an order of magnitude, mainly due to an obsolete value of the Hubble constant, the same calculation today shows a smaller fraction, using greater values for luminous mass. Nonetheless, Zwicky did correctly conclude from his calculation that the bulk of the matter in the Coma cluster was dark matter. Generally though, it is agreed by physicists that dark matter will not play any significant role in regards to the  Far Future of the universe