[Snowdog]

And Sauron urged the King to cut down the White Tree, Nimloth the Fair, that grew in his courts, for it was a memorial of the Eldar and of the light of Valinor.

At the first the King would not assent to this, since he believed that the fortunes of his house were bound up with the Tree, as was forespoken by Tal-Palantir. Thus in his folly he who now hated the Eldar and the Valar vainly clung to the shadow of the old allegiance of Numenor. But when Amandil heard rumour of the evil purpose of Sauron he was grieved to the heart, knowing that in the end Sauron would surely have his will. Then he spoke to Elendil and the sons of Elendil, recalling the tale of the Trees of Valinor; and Isildur said no word, but went out by night and did a deed for which he was afterwards renowned. For he passed alone in disguise to Armenelos and to the courts of the King, which were now forbidden to the Faithful; and he came to the place of the Tree, which was forbidden to all by the orders of Sauron, and the Tree was watched day and night by guards in his service. At that time Nimloth was dark and bore no bloom, for it was late in the autumn, and its winter was nigh; and Isildur passed through the guards and took from the Tree a fruit that hung upon it, and turned to go. But the guard was aroused, and he was assailed, and fought his way out, receiving many wounds; and he escaped, and because he was disguised it was not discovered who had laid hands on the Tree. But Isildur came at last hardly back to Romenna and delivered the fruit to the hands of Amandil, ere his strength failed him. Then the fruit was planted in secret, and it was blessed by Amandil; and a shoot arose from it and sprouted in the spring. But when its first leaf opened then Isildur, who had lain long and come near to death, arose and was troubled no more by his wounds.

Akallabeth

That is the primary word on the character of Isildur. Much less is known of his brother Anarion. I think in deeds of battle Boromir was akin to Isildur in many ways. This character of Isildur is shown again when he takes up the broken sword of Elendil and takes off Sauron's finger with the ring.