Renly Baratheon is the youngest son of Lord Steffon Baratheon and Lady Cassana Estermont. His parents died early in his life during a shipwreck and he was mostly raised by Maester Cressen, while his eldest brother Robert became head of the household. Renly was very young during his brother's rebellion, and was kept safe at Storm's End so he could not be used as a hostage.

Despite being the youngest Baratheon sibling, Robert gave Storm's End, the ancestral seat of House Baratheon, to Renly. This earned him the ire of Stannis, who believed that he was entitled to it. This made Renly powerful, as the lands of Storm's End were bountiful and more resourceful than Dragonstone, which was given to Stannis. During his time at Storm's End, he took Loras Tyrell as a squire, and the two became close friends and eventually lovers.

Renly is handsome and charismatic, earning friends and allies easily, but he is also known to be frivolous. He is said to be the most well-dressed man at court and enjoys tournaments and hunting. He has jet black shoulder-length hair and blue eyes and is said to be the spitting image of his brother Robert in his youth. In battle, he wears a suit of enameled green plate armor and a helmet with a pair of golden antlers.