Benjen Stark was a humble young man, born in the North and fostered in the Reach. He was merry and lighthearted, learning jests and wearing colorful clothes. But when news of his father and oldest brother's death arrived, he grew cold and introspective. He returned North and advised his brother but Eddard being the naive man that he is he sent him to Lys in the search for grain on his journey, Benjen encountered a powerful Lysene sorceress.
After pleasuring her, she admitted to being as old as his father's father due to a magical elixir. Before Benjen could ask more questions, the sorceress threw the elixir at him before disappearing. When Benjen awoke, he found his brother Eddard dead, slain by a faceless assassin's dirk devastated by his brother's death, Benjen cut his long locks of hair, dyed his tresses green and painted his face white and lips red. He found the elixir the sorceress had thrown at him and drank it, unaware of the powers buried within. The elixir caused him to look like fourteen-years-old forever, made him immune to physical damage, and also made him somewhat unhinged.
So Benjen proclaimed himself the Jester, no longer a Stark, and began wandering the land, selling rotten fish and wearing a brightly-colored motley of red, yellow, and wherever he went, Benjen turned the people crazy with a poisonous gaseous concoction that made a laughing riot of the people. He continued on his madcap journey until he reached King's Landing. Before the terrified eyes of the Mad King, Benjen danced and sang a Valyrian lullaby, then advanced on the monarch and hacked off his head. With a wild cry, Benjen threw the head away and kicked the body out of his path, then sat on the Iron Throne and urinated upon it ,With the Iron Throne and many of the royal treasury's valuables, Benjen returned to the North. There he was installed as King-in-the-North, his mad behavior both unassuming and accepted. He continued his original purpose, ensuring the safety of his people, while the non-She-Wolves of the North bicker and fight over the Iron Throne. And so the reign of Benjen the Jester, the green-haired madman, began.