Cardinal is a clerical office in the Roman Catholic Church. Cardinals are counselors of the pope.
Pope Innocent IV granted the use of the red hat to the cardinals in 1245. The red hat was a symbol of the cardinal's readiness to shed their blood in the cause of the church.
The collective name for cardinals is college of cardinals. They meet in a Papal conclave to elect a new Pope.
When there is no pope, the cardinals directs the day-to-day affairs of the Church.
The Coat of Arms of a cardinal who is not a bishop
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"Cardinal (1)". Catholic Encyclopedia. (1913). New York: Robert Appleton Company.