Frederick IX of Denmark was born on March 11, 1899, and became the King of Denmark in 1947. He was the son of King Christian X and Queen Alexandrine. Frederick IX was known for his love of music and sailing, and he played a significant role in modernizing the Danish monarchy during his reign. He ruled until his death on January 14, 1972, and was succeeded by his daughter, Queen Margrethe II. Frederick IX was popular among the Danish people and is remembered for his efforts to strengthen the monarchy's connection with the public and promote national unity.