The main asteroid belt exists between Mars and Jupiter. It also marks the end of the inner solar system and the beginning of the outer solar system. The biggest object in the belt is Ceres.
Ceres is a dwarf planet, though it is much smaller than its closest neighboring dwarf planet, Pluto. Ceres is named after the Roman goddess of agriculture, whose Greek counterpart is Demeter. The Dawn space probe has recently sent us stunning pictures and mountains of data from its 2015 mission to Ceres.
Ceres is heavily cratered, and its most notable feature are its mysterious bright spots. Current data points to these likely being salt deposits, but the mystery still rages.
The next largest resident of the asteroid belt is Vesta. Vesta is not a neatly rounded object like Ceres is, and has a more potato-esque shape. The next largest object is Pallas.