History
We first met Euron Greyjoy in season 6, where he announced himself as a new player by tossing his elder brother Balon, then the ruler of the Iron Islands, off a bridge. Euron was banished from the Iron Islands years ago, and spent the interim as a pirate feared from Oldtown to Qarth. Word is he lost his mind one night at sea, and his crew had to tie him to the mast. When his head cleared, he had the tongues of all his crew members cut out. He needed Silence.
Crazy, calculating and prone to sudden bursts of violence, Euron is the ultimate wild card. After admitting to killing his brother, Euron defeats his niece Yara at the Ironborn Kingsmoot and is elected King of the Iron Islands. However, Yara and Theon manage to steal several valuable ships. Enraged, Euron ordered his new subjects to build a thousand of his own.
Next: Gemma Whelan talks about Yara Greyjoy’s growth into a 'main character'
Status
By now, Euron has presumably built his fleet. He’s likely eager to get his revenge on Yara and Theon, which also puts him at odds with their new ally, Daenerys Targaryen. Euron originally intended to make a marriage alliance with the Dragon Queen, but will now have to look elsewhere.