The Apple of Discord is a magical item that is mentioned in Greek legends.
Accoording to the Greek Legend it appears in, the Apple of Discord was made by the goddess of strife, Eris, to cause discord between the goddesses Athena, Hera and Aphrodite, considered the most beautiful members of the divine pantheon.
In 2014, the apple got locked away in a pearl by a rogue eastern dragon named Drake who conspired with DuLaque. The Eastern Dragons then claimed war as they said the pearl was stolen by the Western Dragons. When the librarians retrieved it from Rome it influenced Jacob and later Cassandra, that almost destroyed the power supply of a large part of Europe until she was brought into her senses.
Whoever holds the apple gets influenced by it. The apple does not change the holder but makes him/her become the worst version they could possibly be of themselves until they drop it.
Ezekiel Jones, while not immune to the effects of the Apple, is seemingly unaffected due to him already being the worst version of himself.