Given the question: Given the following context:  Abaqa died in 1282 and was briefly replaced by his brother Tekuder, who had converted to Islam. Tekuder reversed Abaqa's policy of seeking an alliance with the Franks, offering instead an alliance to the Mamluk Sultan Qalawun, who continued his own advance, capturing the Hospitaller fortress of Margat in 1285, Lattakia in 1287, and the County of Tripoli in 1289. However, Tekuder's pro-Muslim stance was not popular, and in 1284, Abaqa's Buddhist son Arghun, with the support of the Great Khan Kublai, led a revolt and had Tekuder executed. Arghun then revived the idea of an alliance with the West, and sent multiple envoys to Europe.The first of Arghun's embassies was led by Isa Kelemechi, a Nestorian scientist who had been head of Kublai Khan's Office of Western Astronomy. Kelemechi met with Pope Honorius IV in 1285, offering to "remove" the Saracens (Muslims) and divide "the land of Sham, namely Egypt" with the Franks. The second embassy, and probably the most famous, was that of the elderly cleric Rabban Bar Sauma, who had been visiting the Ilkhanate during a remarkable pilgrimage from China to Jerusalem.Through Bar Sauma and other later envoys, such as Buscarello de Ghizolfi, Arghun promised the European leaders that if Jerusalem were conquered, he would have himself baptized and would return Jerusalem to the Christians. Bar Sauma was greeted warmly by the European monarchs, but Western Europe was no longer as interested in the Crusades, and the mission to form an alliance was ultimately fruitless. England did respond by sending a representative, Geoffrey of Langley, who had been a member of Edward I's Crusade 20 years earlier, and was sent to the Mongol court as an ambassador in 1291.  answer the following question:  What is the name of the person whose brother was executed?
The answer is:
Abaqa