One of the worst bad guys in the show, Euron Greyjoy is out of the picture for most of the series. He’s the younger brother of Balon Greyjoy, King of the Iron Islands.
After Balon loses the War of the Five Kings by default, Euron shows up after years in exile and throws him off a bridge to his doom.
Then he shows up to beg the petty lords to vote him as King instead of his niece Yara. He even admits to killing Balon when Yara deduces it was him.
And somehow they crown him King, but Yara’s supporters (which are a lot) flee the Iron Islands with as many ships as they could take away.
While Euron originally wanted to “ally” with Daenerys Targaryen, he instead allies with Cersei Lannister. He ends up killing the Sand Snakes, capturing Yara, and destroying a good majority of the Dragon Queen’s naval forces.
And her dragon Rhaegal is slain by one his giant arrows. Despite all these victories, they’re all rather lame or anti-climatic. Euron isn’t a villain you love to hate, he’s just stupid.
And he dies against Jaime Lannister as the Kingslayer tries to get his sister out of King’s Landing. Which didn’t make much sense honestly. Euron proved himself to be a skilled fighter and beat many brave warriors, but he loses against a right-handed knight with no right hand.