Final answer:
Albert Einstein first suggested the existence of gravitational waves as a consequence of his general theory of relativity. Indirect evidence came from Taylor and Hulse in 1974, and the first direct detection was in 2015 by LIGO.
Step-by-step explanation:
The person who first suggested the existence of gravitational waves was Albert Einstein. He made this prediction based on his theory of general relativity, which describes gravity as the warping of the fabric of space and time by mass. Einstein proposed that massive objects undergoing acceleration, such as two neutron stars spiraling towards each other, would produce ripples in spacetime that propagate outward at the speed of light; these ripples are known as gravitational waves.
Although Einstein predicted their existence, these waves are extremely faint and difficult to detect, resulting in a long quest for direct proof. The first indirect evidence supporting the existence of gravitational waves came from astronomers Joseph Taylor and Russell Hulse in 1974 when they observed a binary pulsar system whose orbit was gradually shrinking, consistent with the emission of gravitational waves predicted by general relativity.
It was not until 2015 that the first direct detection of gravitational waves was achieved by the Laser Interferometer Gravitational-Wave Observatory (LIGO). LIGO picked up waves from the merger of two black holes, providing strong confirmation of Einstein's theory and marking the beginning of a new era in astronomy.