Pope Alexander IV (1199 or c. 1185 25 May 1261) was head of the Catholic Church and ruler of the Papal States from 12 December 1254 to his death in 1261.

Augustinians are members of Christian religious orders that follow the Rule of Saint Augustine, written in about 400 AD by Augustine of Hippo. There are two distinct types of Augustinians in Catholic religious orders dating back to the 12th–13th centuries:

Various congregations of Canons Regular also follow the Rule of Saint Augustine, embrace the evangelical counsels and lead a semi-monastic life, while remaining committed to pastoral care appropriate to their primary vocation as priests. They generally form one large community which might serve parishes in the vicinity, and are organized into autonomous congregations.

Several orders of friars who live a mixed religious life of contemplation and apostolic ministry. The largest and most familiar is the Order of Saint Augustine (OSA), founded in 1244 and originally known as the Hermits of Saint Augustine (OESA). They are commonly known as the Austin Friars in England. Two other orders, the Order of Augustinian Recollects and the Discalced Augustinians, were once part of the OSA under a single prior general. The Recollects, founded in 1588 as a reform movement in Spain, became autonomous in 1612. The Discalceds became an independent congregation in 1592, and were raised to the status of a separate mendicant order in 1610.There are also some Anglican religious orders created in the 19th century that follow Augustine's rule. These are composed only of women in several different communities of Augustinian nuns.