Short answers, pulled from the story.
The asteroid belt was first discovered on the 1st of January 1801 when Giuseppe Piazzi observed a tiny moving object from Palermo, Sicily. This discovery confirmed Johannes Kepler's theoretical prediction from 1596 that an invisible world must exist in this region to fill the gap in planetary spacing.
The asteroid belt formed from the primordial solar nebula as a group of planetesimals that clumped together through sticky collisions during the first few million years of Solar System history. Strong gravitational perturbations from Jupiter disrupted their accretion into a single planet, causing most material to be ejected within about one million years of formation.
The present day belt consists primarily of C-type carbonaceous asteroids dominating outer regions, S-type silicate-rich asteroids common toward the inner region, and M-type metal-rich asteroids occupying the middle of the main belt. Carbonaceous C-type asteroids comprise over seventy-five percent of visible asteroids while S-type asteroids form about seventeen percent of the total population.
Kirkwood gaps occur where revolution periods form an integer fraction of Jupiter's orbital period with the 4:1 orbital resonance at radius 2.06 AU serving as the inner boundary of the main belt. The core region lies between strong 4:1 and 2:1 Kirkwood gaps at 2.06 and 3.27 AU containing ninety-three percent of all discovered minor planets as of the 8th of February 2006.
Pioneer 10 became the first spacecraft to traverse the asteroid belt on the 16th of July 1972 followed by multiple probes including Voyager 1 and 2 Ulysses Cassini Juno and Dawn that crossed the region safely. The Dawn mission orbited Vesta between July 2011 and September 2012 before moving to Ceres where it has orbited since March 2015 studying surface features extensively.