ideas for more great diplomats:
Johann Rudolf Wettstein (Swiss Mayor of Basel who showed up to the Wesphalian peace negotiations uninvited and unaccredited, and successfully negotiate Switzerland's independence at the conference)
Pope Leo I (The pope that met with Attila and negotiated for him to stop his invasion of Italy)
Ibrahim Pasha (Grand Vizier of the Ottoman Empire under Suleiman the Magnificent. Negotiated an alliance between the Ottomans and France against Spain, and negotiated for Hungary to become a vassal of the Ottomans without a war)
Jose Maria da Silva Paranhos (Diplomat for Brazil to Germany, Foreign Affairs Minister for both the empire and nation of Brazil. Negotiated the modern borders of Brazil with Paraguay, French Guiana, Argentina, and Bolivia. It can be argued that his successful diplomacy gave Brazil complete control of the entire Amazonian basin, and he gained entire provinces of land for Brazil in exchange for relatively minor concessions)
Moshoeshoe I (founder of Lesotho. Through tactics, intelligence, negotiation and persuasion, he forged alliances with many smaller African and refugees from the destabilization caused by the growth of the expanding Zulu empire. He created the kingdom of Lesotho, resisting the expansion of Afrikaaners, and his kingdom survives to this day. The prototypical pan-Africanist)
Jigonhsasee (Along with Hiawatha and the Great Peacemaker, created the Great Law of Peace which brought together the 5 nations to form the Haudenosaunee (Iroquois))
Kamehameha III (modernized the constitution and, through diplomatic means, ensured the survival of the kingdom of Hawai'i from various imperial interests)
Kosa Pan (The second Envoy sent from Siam to France. Established the Siamese embassy in France, had audiences with the Pope and Louis XIV. solidified French-Siamese alliance)