Who started All Saints Day?

Answer 1

The origin of the festival of All Saints as celebrated in the West dates to May 13, 609 or 610, when Pope Boniface IV consecrated the Pantheon at Rome to the Blessed Virgin and all the martyrs; the feast of the dedicatio Sanctae Mariae ad Martyres has been celebrated at Rome ever since. The chosen day, May 13, was a pagan observation of great antiquity, the culmination of three days of the Feast of the Lemures, in which the malevolent and restless spirits of the dead were propitiated. Liturgiologists of the Middle Ages based the idea that this Lemuria festival was the origin of that of All Saints on their identical dates and on the similar theme of "all the dead".

The feast of All Saints, on its current date, is traced to the foundation by Pope Gregory III (731-741) of an oratory in St. Peter's for the relics "of the holy apostles and of all saints, martyrs and confessors, of all the just made perfect who are at rest throughout the world", with the day moved to November 1.