Aragorn is one of the most heroic figures in The Lord of the Rings legends, as he fought alongside Gandalf and Frodo to destroy the One Ring and was the true heir of Gondor. However, as a Dúnedain, Aragorn lived three times longer than the average man. And since he outlived the ending of Return of the King, to find out how the king died, one must consult Tolkien's books.
In the movies, Aragorn, played by Viggo Mortensen, was a mythical warrior that was destined to become the true King of Gondor. By the trilogy's conclusion, he was also crowned the King of Arnor and the first High King of the Reunited Kingdom. As told in The Tale of Aragorn and Arwen, Aragon fell in love with an immortal elf maiden named Arwen, whose father forbade her marriage to a mortal until he became King of Arnor and Gondor.
Once these conditions were met, Aragorn and Arwen were married and lived a happy and prosperous life as king and queen for 120 years. At the age of 210, Aragorn felt that he had lived enough life and wisely chose to die. As a descendent of the Númenoreans, a legendary and virile breed of man, Aragorn could choose when he wanted to die, without the need to carry out a violent suicide. He was a wise king, who knew that death was nothing to fear and that all life must come to an end.
After discussing his decision with his wife, Arwen, who gave up her immortality to be with him, Aragorn named his son, Eldarion, the next ruler of Gondor and Arnor. He then laid himself down in his tomb in The House of Kings in the Silent Street and gave his son the winged crown of Gondor and the scepter of Arnor. Arwen remained by his side, as he willed himself to die a peaceful sleep, letting his spirit slip away beyond the mortal boundary of the Circles of the World. Despondent after her husband's death, Arwen wandered into the woods of Lorien and died of old age herself.
Aragorn died as he lived, a wise and graceful leader amongst men. He is remembered as a valorous warrior in his youth and a sage king in his old age. It takes great insight and courage to give up the throne when one feels they cannot carry out the duties effectively anymore. Aragorn felt content with his life and understood that it was better to die with dignity than live with depravity. While Arwen was still bitter over her mortality, Aragorn depicted Tolkien's theme of death as being a natural part of life.
Aragorn's quiet death does not take away from his long and legendary life of noble wars and flourishing reigns. In truth, him taking control of his own destiny is the most honorable way a king could leave Middle-earth.