Short answers, pulled from the story.
Marcus Vipsanius Agrippa began construction of the original Pantheon between 29 and 19 BC as part of a building program on his own property. The current structure is not the one Agrippa built because the original temple burned down completely except for its façade during a fire in 80 AD.
The present construction likely began around 114 under Emperor Trajan four years after the second fire destroyed the previous version. Lise Hetland argues that the commonly maintained Hadrianic date should be reexamined based on brick-stamp studies which suggest Herbert Bloch excluded all Trajanic-era bricks incorrectly in 1959.
In 609 Byzantine emperor Phocas gave the building to Pope Boniface IV who converted it into a Christian church. On the 13th of May 609 he consecrated it to St. Mary and the Martyrs and placed twenty-eight cartloads of holy relics from catacombs beneath the high altar.
The height to the oculus and the diameter of the interior circle are both 43.3 meters meaning the whole interior fits exactly within a cube or sphere of that same dimension. The dome spans 150 Roman feet while the oculus measures 30 Roman feet in diameter with thickness varying from 6 meters at the base to 1 meter around the opening.
Raphael lies buried here with his fiancée Maria Bibbiena who died before they could marry and King Victor Emmanuel II died in 1878 and rests in a chapel originally dedicated to the Holy Spirit. Manfredo Manfredi won a competition to design this tomb starting work in 1885 and other notable burials include Annibale Carracci Arcangelo Corelli and Baldassare Peruzzi.