Tycho Nestoris is a representative of the Iron Bank of Braavos. He is a rational man, more interested in numbers than in words, reasoning that the former are less likely to deceive than the latter.
Shortly after Tommen Baratheon's coronation, Tycho and two of his colleagues receive Stannis Baratheon and his Hand, Ser Davos Seaworth, who ask them to fund their continuing campaign in Westeros. Tycho points out their weak position and is ready to dismiss them when Ser Davos speaks up, relating how he came into Stannis' service, how the latter is a just man who keeps his word, and how he is the best chance for the Iron Bank to get its money back upon the chaos that would follow the death of the elderly Tywin Lannister. This seems to convince the banker and his colleagues, as they agree to fund Stannis.
Tycho receives Mace Tyrell when the latter arrives in Braavos to renegotiate the kingdom's terms with the Iron Bank. Though polite, Tycho seems to dislike Tyrell, whose bumbleness clashes with Tycho's polite dignity. On the way to the bank, Mace offers him fine wines from the Arbor as a token of esteem but Tycho politely declines. After negotiating with Mace for some time, Tycho leads his guest outside to bid him farewell, but Mace keeps talking, stating that singing is a skill that anyone can learn. To prove that, he immediately starts singing a song, much to Tychos disapproval.
After Cersei Lannister's coronation, Tycho is sent to Westeros in order to get back the money the Crown owes the Iron Bank. He meets with Cersei and the two discuss Cersei's position in the world and in the war against Daenerys Targaryen. During the conversation, Tycho admits that the Iron Bank had made strong profits in the slave trade which has now been destroyed by Daenerys. Cersei actually manages to convince Tycho to stay in King's Landing for a fortnight - promising that he will return to Braavos with her debt paid in full.
Tycho meets with Cersei for a second time, who compliments her for paying back much of her massive debts in a single payment, noting that he does not believe the Iron Bank has ever been paid back in such a manner. He flatters Cersei by telling her that she seems to be almost surpassing her father in this regard; Cersei thanks him for his kindness, addressing him as a lord, but Tycho points out he is neither kind nor a lord, but merely an employee of the Iron Bank. Tycho tells Cersei that some of his colleagues may be disappointed as they were interested in bringing up Cersei's interest rates. Nonetheless, he suggest that the Iron Bank may be able to invest in Cersei's venture to reestablish her control over the Seven Kingdoms. Cersei informs Tycho that her Hand, Qyburn, has reached out to the Golden Company, a powerful sellsword company in Essos. Tycho assures Cersei that they will support the Iron Throne - once they get their gold.
A banker with the iron Bank of Braavosa, Tycho Nestoris is very aware of the political situation in Westeros.