Short answers, pulled from the story.
The word cardinal derives from the Latin term cardo, meaning hinge or pivot, which reveals the office's original function as the essential support upon which the Church turned. In the early sixth century, the first individuals to bear this title were the deacons of the seven regions of Rome, tasked with administering the city's charitable works and liturgical duties.
Pope Innocent IV granted the red hat, or galero, to cardinals in 1244. This distinctive wide-brimmed hat was discontinued as a physical garment in 1969, yet it remains a permanent fixture in ecclesiastical heraldry with fifteen tassels on each side to denote the cardinal's rank.
Pope Paul VI established that only cardinals under the age of 80 could participate in the election of a successor, a rule that took effect on the 1st of January 1971. This regulation immediately deprived 25 cardinals of their voting rights to ensure the College remained a body of active, working-age leaders.
Cardinal Henry of Portugal was crowned king, representing the only example of a cardinal-king in history. Other crown cardinals like Cardinal Richelieu and Cardinal Wolsey wielded influence that rivaled monarchs, but Henry was the sole instance of a cardinal ascending to the throne.
The College of Cardinals is divided into three distinct orders: cardinal bishops, cardinal priests, and cardinal deacons. Cardinal bishops include six Latin Church cardinal bishops of the suburbicarian sees and patriarchs of the Eastern Catholic Churches, while cardinal deacons consist mainly of officials of the Roman Curia.
The last pope known to have named a cardinal in pectore was Pope John Paul II, who named four such cardinals in 1998. One of these four remains unidentified to this day, and if a pope dies before revealing the identity of a secret cardinal, the appointment expires.