Chaos
Chaos is part of the philosophical system of Ultima Online, namely the Virtues. It was created by Lord Blackthorn as a counter to Lord British's system of Virtues. It stresses individuality and difference. Several in-game books describe the philosophy further.
For many years, Chaos and Virtue (called "Order") was a PvP system within the game, similar to guild wars or factions.
According to an in-game book by Sherry the Mouse, Blackthorn supposedly invented Chaos after overhearing a conversation wherein it was revealed that Lord British, the King of Britannia, wished to get everyone to follow the Virtues, even though this would result in integration of the shards. Lord Blackthorn feared that integration would mean that the people living on each shard would be basically blinked out of existence. Therefore, he created Chaos to help insure that Virtue would literally never conquer all. As long as one person followed Chaos instead, the shards would never be integrated.
Some of Blackthorn's writings, for example note "On the Diversity of Our Land," make it clear that Blackthorn would extend fundamental rights to such creatures as Orcs. After Blackthorn turned evil, partially under the influence of Exodus, Chaos took on a more sinister overtone than diversity and difference. It became one of the lack of moral standards, decay, murder, and death.
Some of the role-played legislatures known as High Councils that have cropped up on certain shards incorporate a seat for Chaos, usually either called the Seat of Chaos (on Lake Superior for example) or Seat of Balance.