Short answers, pulled from the story.
Gravity is a fundamental interaction that draws material objects toward each other in proportion to their masses and inversely to the square of the distance between them. It is one of the four fundamental interactions, and it has infinite range, though its effects weaken with distance. Gravity becomes the dominant interaction at the scale of astronomical bodies, governing satellites, planets, stars, galaxies, and even light.
Albert Einstein proposed the general theory of relativity in 1915. It describes gravity as the curvature of spacetime caused by the uneven distribution of mass, and it accurately modeled Mercury's orbit where Newton's theory had failed.
Isaac Newton described gravity as a universal attractive force between any two bodies, proportional to the product of their masses and inversely proportional to the square of the distance between them. He published this in Philosophiæ Naturalis Principia Mathematica, unifying Earth-bound acceleration with celestial mechanics and concluding that the gravity of the Earth on the Moon is the same as on an apple.
Gravitational waves were first directly detected on the 14th of September 2015 by the LIGO detectors. The waves came from the collision of two black holes 1.3 billion light years from Earth, and this research was awarded the Nobel Prize in Physics in 2017.
Gravity is incompatible with quantum mechanics because general relativity describes it as a smooth, continuous distortion of spacetime, while quantum mechanics holds that forces arise from the exchange of discrete particles called quanta. The other three fundamental forces were reconciled with a quantum framework decades ago, but the graviton approach to gravity fails at distances of the order of the Planck length.
Gravity drives star formation by pulling hydrogen gas together until it reaches pressures sufficient for nuclear fusion. When a star's fuel runs out, its fate depends on mass: low mass stars become white dwarfs, while higher mass stars explode as supernovae and leave behind neutron stars or black holes, where gravity operates so intensely that even light cannot escape.