Who is Isildur from Unfinished Tales of Numenor and Middle-earth and what is their importance?

Isildur is the man who manages to cut the Ring of Power from Sauron's finger. He is unable to destroy the ring and tries to take it back to Gondor with him. During the journey, his army is attacked and no match for the force that they face. Isildur tries to retreat with the ring, but it slips from his finger. He is killed by orc arrows. Isildur's inability to destroy the ring is looked upon as the weakness of man.