Pendant of Courage
"Ancient Hylian lore states that only the person who wears the Pendants of Courage, Power and Wisdom can become the Hero. It has also been said that only the Hero can wield the Master Sword. The three Pendants are the key to unlocking the Master Sword from the stone in which it has been embedded for eons. When Link obtains all three Pendants, he should go to the Lost Woods and find the Master Sword. After obtaining the powerful work of art, he can go after the root of the evil."
A Link to the Past
The Pendant of Courage is the green-colored and first pendant found in A Link to the Past. It is found within the Eastern Palace. It is acquired by defeating the Armos Knights. Once they have been defeated, Link is bestowed the Pendant.
With the Pendant of Courage, Link can head down to Sahasrahla's house in the Eastern Palace Grounds. As a reward for acquiring the pendant, Sahasrahla gives Link the Pegasus Boots.
The Pendant is one of three Pendants of Virtues, all three of which are required to obtain the Master Sword.
A Link Between Worlds
The Pendant of Courage returns in A Link Between Worlds. The Pendant of Courage, along with the Pendant of Wisdom and the Pendant of Power, is needed in order for Link to obtain the Master Sword. The Pendant of Courage is given to Link by Princess Zelda very early in the game.