Which pope designated November 1st as All Saints Day?

Answer 1

From Wikipedia:

The origin of the festival of All Saints celebrated in the West dates to May 13, 609 or 610, (see Pope Boniface link below) consecrated the (see Pantheon in Rome note below) 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 feast of All Saints, on its current date, is traced to the foundation by (see link for Pope Gregory below) (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.

Catholic Answerfrom Encyclopedia of Catholic Devotions and Practices by Ann Ball, Our Sunday Visitor, Inc. C 2003

All Saints Day A holy day of obligation, November 1, commemorating all the blessed in heaven; intended particularly to honor those who have no special feasts.

In the fourth century, groups of martyrs, and later other saints, were honored on a common day in various places. In 609 or 610, the Pantheon, a pagan temple in Rome, was consecrated as a Christian Church in honor of Mary and the martyrs and, later, all saints. In 835, Pope Gregory IV fixed November 1 as the date of the observance.

Answer 2

Pope Gregory the third started it. Gregory the fourth finally designated November 2 All Saint's Day. They moved it from May 13 to November 1.

Answer 3

The feast of All Saints, on its current date of November 1, is traced to Pope Gregory III (731-741).