Atreus and Thyestes did not get along. (Wow, there's the understatement of the year.) These brothers hated each other so much in life, we bet they're still coming up with awful things to do to each other down in the Underworld. The bad blood between these dudes was so bad (and the legend is so old) that their horribly destructive relationship has become synonymous with the idea of "sibling rivalry." Throughout the centuries, the brutal feud between these brothers has been used as a reference point for all the dueling brothers to come.