The only reason why the Catholic Church still feels that Saint Callistus, sometimes spelled Calixtus, actually existed is because he was the Roman Pontiff from the years 217-222 A.D. The year of his birth is completely unknown.
The Church has only one biography of Callistus and this was written by his lifelong nemesis Saint Hippolytus of Rome (c. 170-c. 236). Consequently, Callistus’ faults are often exaggerated and there is very little information about his real life.
According to tradition, Saint Callistus was the slave of a Christian man named Carpophorus. Callistus was placed in charge of a bank owned by his master. Through some unknown cause, Callistus lost all of his master’s money and ran away to escape punishment. Although the real cause is completely unknown, it is widely accepted that Callistus was not a thief.
Callistus was caught near Rome and was sentenced to several years of hard labor. He was later rescued from this fate when his master’s clients pleaded his innocence.
The future Pope did not remain free for long, however. Shortly after his release, he was sent to a synagogue to collect money from his master’s Jewish clients. What exactly happened is not known but a brawl broke out and Callistus was sent to the mines of Sardinia. He was later released when Marcia (unknown-193), the Christian mistress of the Emperor Commodus (161-192) used her influence with the Emperor at the request of Pope Victor I (unknown-199).
Callistus gained his freedom after his release from the mines and, at the request of the new Pope Saint Zephyrinus (unknown-217), became the overseer of a local Christian burial ground known now as the Cemetery of Saint Callistus.
After the death of Pope Zephyrinus, Callistus was elected Roman Pontiff by an almost unanimous vote. His only rival had been Hippolytus. The two men crossed swords an almost unbelievable number of times over strange theological problems that are not even discussed anymore. Hippolytus even went so far as to call Callistus a heretic.
Little is known about the papacy of Callistus I except that he wrote two epistles. How he died is also unknown. It is thought that he might have been thrown down a well by pagan enemies during the year 222. Consequently, he is sometimes venerated as a martyr.
Pope Saint Callistus I is considered the patron saint of cemetery workers. His feast day is October 14.
Source: Butler’s Lives of the Saints