The answer is St. Ignatius of Loyola.
Catholic Answer
There were many leaders during the Counter-reformation:
The Counter-Reformation is the name given to the Catholic movement of reform and activity which lasted for about one hundred years from the beginning of the Council of Trent (q.v., 1545). Popes St. Pius V and Gregory XIII, Philip Neri, Charles Borromeo, St. Ignatius
from A Catholic Dictionary, edited by Donald Attwater, Second edition, revised 1957The Counter-Reformation is the name given to the Catholic movement of reform and activity which lasted for about one hundred years from the beginning of the Council of Trent (q.v., 1545), and was the belated answer to the threatening confusion and increasing attacks of the previous years. It was the work principally of the Popes St. Pius V and Gregory XIII and the Council itself in the sphere of authority, of SS. Philip Neri and Charles Borromeo in the reform of the clergy and of life, of St. Ignatius and the Jesuits in apostolic activity of St. Francis Xavier in foreign missions, and of St. Teresa in the purely contemplative life which lies behind them all. But these were not the only names nor was it a movement of a few only; the whole Church emerged from the 15th century purified and revivified. On the other hand, it was a reformation rather than a restoration; the unity of western Christendom was destroyed; the Church militant (those still on earth) led by the Company of Jesus adopted offence as the best means of defence and, though she gained as much as she lost in some sense, the Church did not recover the exercise of her former spiritual supremacy in actuality.
Martin Luther, a German monk, was a leader in the Protestant Reformation, challenging the Catholic Church's teachings and practices in the 16th century. His actions led to the formation of new Christian denominations.
The religion with a spiritual leader known as the pope is Christianity, specifically the Roman Catholic Church. The pope is considered the leader of the worldwide Catholic Church and is based in Vatican City.
The Reformation, led by Martin Luther and others, sought to reform the Catholic Church and ultimately led to the formation of Protestant denominations. The Counter-Reformation was the Catholic Church's response to the Reformation, focusing on reforming itself, reaffirming Catholic doctrine, and combating the spread of Protestantism.
No, St. Francis of Assisi was not a Church leader in terms of holding positions of authority within the hierarchy of the Catholic Church. He was a well-known Catholic friar and founder of the Franciscan Order known for his humility, simplicity, and devotion to serving the poor and marginalized.
There is no canonized saint named Darren in the Catholic Church. Saints in the Catholic Church are individuals who have been officially recognized for their holiness, virtue, and miracles.
It seems there may be a typo in your question. If you are asking about "Catholic," it is a denomination of Christianity that follows the teachings of Jesus Christ as passed down through the Apostles and interpreted by the Magisterium of the Catholic Church.
Erasmus advocated reforming the catholic church
The Reformation was devoted to reforming the Catholic Church.
The pope in Rome is the leader of the entire Catholic Church.
There have been untold leaders that have reformed the Catholic Church in the past 2,000 years. The very nature of the Church is to be reformed as it is composed entirely of sinners (saving Our Blessed Lord, and His Mother). So to get a specific answer to your question, you are going to have to narrow it down to a time period, and perhaps a country.
Huldrych Zwingli was the leader of the Protestant Reformation in Zurich. He was a Swiss priest who believed in reforming the Catholic Church through his teachings and writings. Zwingli's ideas laid the foundation for the development of Protestantism in Switzerland.
The Catholic Church did not exist in 4 BC.
The Roman Catholic Church
The pope is the leader of the catholic Church on earth.
Pope Francis is the supreme leader of the Catholic Church.
The leader of the Catholic Church is the pope. Today (2011) that is Pope Benedict XVI.
Erasmus advocated reforming the catholic church
The pope in Rome, today that would be Pope Benedict XVI, is the leader of the ENTIRE Catholic Church, even in Russia.