Gregory IV, pope (827-844), was chosen to succeed Valentinus in December 827, on which occasion he recognized the supremacy of the Frankish emperor Louis the Pious in the most unequivocal manner. His name is chiefly associated with the quarrels betweeen Lothar and Louis the Debonaire, in whom he espoused the cause of the former, for whom, in the Campus Mendacii, or "field of lies" as it is usually called (833), he secured by his treachery a temporary advantage. The institution of the feast of All Saints is usually attributed to this pope. He died January 25, 844, and was succeeded by Sergius II.
from the 9th edition (1880) of an unnamed encyclopedia