|The title of this article is conjecture based on information revealed in the A Song of Ice and Fire novels or related material and may be subject to change.
- "When I was a boy of sixteen a great lord caught me with his mistress. He should have been honored, instead the fat old fool challenged me to a duel. Thanks to my age and status, only to first blood. But his mistress... and his wife, warned me which of my parts he intended to draw first blood from."
- ―Oberyn Martell
Edgar Yronwood was a Dornish lord, and the head of House Yronwood.
In his youth, Prince Oberyn Martell was fostered by Lord Yronwood at Yronwood. When Oberyn was sixteen, he was found abed with Lord Edgar's mistress. Edgar challenged the prince to a duel, though only to first blood due to Oberyn's youth and high birth. Both men took cuts and honor was satisfied. However, while Prince Oberyn soon recovered, Edgar's wounds festered and he died. Afterward it was rumored that Oberyn had poisoned his sword, gaining his nickname of "The Red Viper". 
In the books
In the A Song of Ice and Fire novels Edgar Yronwood's backstory is much the same. In the TV continuity, however it is implied that Oberyn had slept with Edgar's wife as well as his paramour.