Euron Greyjoy has a reputation for being mad.
Among a House and people of outcasts, he is outcast himself, warned never to return to the Iron Isles by command of his own brothers. They think they know why, and certainly he won't deny their claim—he did take his brother Victarion's woman, just as he's taken a great many others over the years, as if there were any difference. The other whispers about him, his evil eye and mad blue smile, his unpredictability and vicious temper, all of those are true too. But they're none of them the real reason Euron Greyjoy is outcast, and when he thinks about it he laughs.
Euron Greyjoy is outcast because he knows.
He knows what the Iron Islands have forgotten, what the Greyjoys pay pale homage to with their sigil and what the Drowned Men pay lip service to in their baptisms. All Ironborn know the words, of course, initiation rite and battle cry and funeral litany: "What is dead may never die." Euron Greyjoy knows where the words came from. Were bastardized from. He's sailed to doomed Valyria and back again, shattered and smoking and sunken. He's learned the true words, correct and complete, though only as accurate as human tongues could shape them.
Throughout Westeros and Essos both there's talk of Winter coming, of magic returning and dragons waking and the frozen dead rising to walk again. The Gods have returned, they say, and Euron and his ship of muted and mutilated men have seen their true shape.
Stranger aeons, he thinks to himself, as he turns the Silence toward home once more. Indeed.
The men and women of the Iron Islands may play at worship of their Drowned God, but Euron Greyjoy knows its name.