Mero
The Titan's Bastard: a huge, vicious captain of the Second Sons, a boastful drunk who badly underestimates the dragon queen he's hired to fight.
The fuller tale
Mero of Braavos, called the Titan’s Bastard, commands the Second Sons when the tale brings the company to Yunkai’s defense — a huge, red-bearded sellsword with a reputation foul enough that Braavos itself expelled him, and manners calculated to prove the reputation modest. His parley with Daenerys is a small masterpiece of self-sabotage: invited to treat, he drinks her wine, leers at her body, insults her to her face, and saunters out convinced he has taken the measure of a girl playing at war. He has, in fact, been measured himself — by the queen, by her captains, and most consequentially by his own lieutenant, who is doing arithmetic of a different kind.
He exists in the story to embody the sellsword trade at its most honest: no banners, no pieties, loyalty priced by the day and revocable by the hour. The joke the tale plays is that this cynicism, which Mero believes makes him unkillable, is precisely what kills him — a company that follows coin rather than men will follow it out from under its own captain. Between the wine and the morning, Daario Naharis puts the company’s logic to its natural conclusion, and the Second Sons change owners the way their contracts always said they would.
The books give Mero a longer, meaner coda than the show’s clean cut, letting him slip the battle and come back for vengeance weeks later with a beggar’s disguise and a knife — a reminder, characteristic of the novels, that loose sellswords do not simply vanish when the plot moves on.
The page and the screen
In the show Mero commands the Second Sons with Prendahl and Daario as his lieutenants, and dies off-screen the night Daario changes sides — his head arriving in a sack at Daenerys’s feet along with Prendahl’s. The books arrange the companies differently: Mero’s Second Sons and Prendahl’s Stormcrows are separate outfits in Yunkai’s pay, Daario belongs to the Stormcrows, and Mero survives the turning entirely — his company routed, the Titan’s Bastard escapes and goes to ground. He resurfaces in A Storm of Swords hidden among the beggars of Meereen’s road, springing at Daenerys with a knife when she walks among her freedmen; Strong Belwas, her eunuch guardian, takes the blade across his belly and guts Mero in the dust, then complains at length about the scar. Same man, two deaths: the show’s a line item in Daario’s courtship, the books’ a lesson in what unpaid grudges do between chapters.
Where they stand, season by season
Their fate — if death has found them, it is written here. Open at your peril.
The show: His head answered Daario's ambition (S3·E8)
The books: Gutted by Strong Belwas (ASOS, ch. 60)
The Titan's Bastard drank, spat, and plotted to murder the dragon queen he was paid to fight. Daario Naharis chose a different employer and delivered his captains' heads to Daenerys's feet.
The show’s Mero dies the night the Second Sons change allegiance: sent with Prendahl and Daario to settle which of them will murder the dragon queen for Yunkai’s gold, he is instead settled himself — Daario kills both his captains and delivers their heads to Daenerys’s tent in a sack, laying the company’s swords at her feet with the trophies. The books kill him later and better: escaped from the rout at Yunkai, Mero stalks Daenerys to Meereen disguised as one of the begging brothers along her road, and lunges from the crowd with a knife when she passes close. Strong Belwas takes the thrust across his belly to reach him and opens the Titan’s Bastard from groin to gullet in front of the crowd — then, in the books’ perfect grace note, grumbles that Mero has spoiled the symmetry of his scars. In both tellings the moral is identical and entirely sellsword: he underestimated everyone in the story exactly once.