Lewyn Martell

Ser 'Lewyn Martell was a knight in the Kingsguard of King Aerys II Targaryen, who became known as "the Mad King".

Background
Ser Lewyn Martell was the uncle of Doran, Oberyn, and Elia Martell. A younger son, he joined the elite Kingsguard, forswearing any claim to land and title.

During Robert's Rebellion, at the climactic Battle of the Trident, Ser Lewyn accompanied fellow Kingsguard Ser Barristan Selmy and Crown Prince Rhaegar Targaryen to face the rebel army led by Robert Baratheon. Ser Lewyn perished in the battle, along with thousands of other Dornishmen.

In the books
In A Song of Ice and Fire, Lewyn Martell is remembered fondly by his family as a kind man who loved his extended family. The Kingsguard are forbidden to marry or even to love, and in the past several have been severely punished even for having sexual affairs. As per the customs of Dorne, however, Ser Lewyn continued to secretly keep a paramour. Ser Barristan and the other Kingsguard were aware of it but kept his secret, as he did not let it interfere with his duty.

At the Battle of the Trident, Ser Lewyn led the large Dornish continent (10,000 men strong) which threatened to break Robert Baratheon's left flank. During the fighting Ser Lewyn became badly wounded, however, and in the confusion Ser Lyn Corbray led a counter-charge by the rebels, in which he personally dueled killed Lewyn Martell. Ser Lyn - vain, arrogant, and secretly a pedophile - would in later years boast about how he had personally defeated Ser Lewyn, though in reality Ser Lewyn was already very badly wounded (perhaps mortally so) and Corbray simply finished him off.