The Apple of Discord was the object used by Eris, the goddess of chaos, to cause discord among the gods. It began when Eris was not invited to a wedding between Thetis and Peleus. Infuriated by this, she tossed a solid gold apple into the wedding. It had inscribed on it "TO THE FAIREST". All of the gods recoiled and most goddesses, but Athena, Aphrodite, and Hera fought over the title in a show of vanity. They asked Zeus who it belonged to, and he responded to ask Paris, a mortal prince. They showed him the Apple, and asked the question, bribing him with gifts. He chose Aphrodite, and would cause war between the gods and mortals, and being the Trojan War.
The Golden Apples are known in the Greek Mythology to give immortality to anyone who eats them, however, since the gods and goddesses are all immortal, Athena, Hera and Aphrodite only fought over the apple for the title of Fairiest. The Golden Apples have a similar function to the Forbidden Fruit in the Garden of Eden.
In fact, many theorize that they are possibly one in the same. According to Gabriel, a being by the name of Hesperus whom is the personification of the Evening Star and the son Eos, the goddess of the dawn, was able to achieve the gardening knowledge and the type of flora used and planted in the Garden. As such, he succeeded in building a near replica of the Garden of Eden known as the Garden of Hesperus. Zariel believes that Hesperus was in fact an angel and actually being a sliver of Lucifer himself, whom was identified as Phosphorus, the "Morning Star."