Pope Leo I

• Historians consider Pope Leo I, who ruled from 420 to 461, to be the first pope. After claiming authority over the Christian world, he used his authority to resolve doctrinal and jurisdictional disputes, further establishing the papacy as the ultimate word. Known for his diplomatic skills, Leo I twice helped to save Rome, first from advancing armies of Huns (452) and later, from the destruction of the city by Vandals (455). Pope Leo I, who was later canonized, also played a major role in extending the jurisdiction of his papacy over Gaul, Spain and North Africa.
  
  

Charlemagne

• Crowned by Pope Leo III as emperor of the Romans, Charlemagne (742 to 814) gets credit for expanding the dominion of the Holy Roman Empire militarily, and by encouraging learning and the order of law throughout his vast realm. This in itself helped to create Western Civilization. Considered one of the greatest military leaders in history, Charlemagne's led military campaigns against the Saxons (772 to 804) and Huns (791 to 795) and dramatically expanded Christendom's reach to the east.
  
  

Thomas Aquinas

• Thomas Aquinas (1225 to 1274) is one of the most important philosophical and theological minds in the history of Roman Catholicism. Aquinas' devotion to God and learning began as a child and culminated in his masterwork, Summa Theologica, a groundbreaking treatise on reason and religion and comparison of Aristotelian thought with the Bible. During the 17th and 18th centuries, the school of theological thought known as Thomism fell out of favor in European theology, but Pope Leo XIII resurrected it in 1889 and it has remained central to Roman Catholic theology. Thomas Aquinas was canonized by Pope John XXII in 1323.
  
  

Hugh de Payens and the Knights Templar

• Hugh de Payens founded the order of the Knights Templar in 1115 to protect Christians on pilgrimage to Jerusalem. Based at Jerusalem's Temple of Solomon, the Templars quickly grew in number as word of their exploits circulated in Europe. The Knights Templar soon gained a reputation as one of the 12th century's most formidable military forces in the Holy Land. Originally bound by a vow of poverty, as the order's original name -- The Poor Knights of Christ -- suggests, the Templar's had amassed fabulous wealth by the 13th century. The order fell out of favor with the church in the late 1200s and it was finally disbanded in 1312.