The common traits among all these men include intelligence, coherence, mercy and prudence at decision-making. They are "created” during a special ceremony called a "consistory.” The last one took place on November 2012, where Benedict XVI created six new cardinals. In all, there a currently 207.
Their main function is to advise the Pope, hence why many preside over the most important departments of the Roman Curia or the largest dioceses in the world.
But their most important function is to elect the new Pope during the Sede Vacante period.
The College of Cardinals is broken down into three orders. The Cardinal Bishops hold the highest rank. The eastern patriarchs are among this group. The leader among them is the Cardinal Dean, who is considered the primus inter pares, first among equals. That was the honor Joseph Ratzinger had before being elected Pope.
Currently, the Cardinal dean is Angelo Sodano, and the Vice-Dean is Roger Etchegaray, both are required to live in Rome. Both are also over 80 years old and cannot vote in the conclave.
The second order are the Cardinal Priests, who make up the majority. They represent the universality of the Church and tend to lead the world's largest archdioceses.
The third and last order are the Cardinal Deacons and are chosen from various fields of work. Among them is the Cardinal Proto-Deacon cardinal, the eldest of which is the one that steps out into the balcony at St. Peter's Square to present the new Pope. Currently, French Cardinal Jean-Louis Tauran holds this post.
Red, the color of the cardinals, symbolizes their willingness to die for their faith. They also receive a ring, the gift from the Pope signifying their marriage with the Church. On the inside, the crest of the Pope that created them is engraved.
The cardinals eligible to vote are only those that are under 80 years old at the start of the papal vacancy. They take an oath to vote by conscience for the person they consider best fit to be the Successor of Peter. This time around there are 117 eligible to vote.