John III Doukas Vatatzes, Latinized as Ducas Vatatzes (, Iōannēs Doukas Vatatzēs, c. 1192 – 3 November 1254), was Emperor of Nicaea from 1221 to 1254. He was succeeded by his son, known as Theodore II Laskaris. Life John Doukas Vatatzes, born in about 1192 in Didymoteicho, was probably the son of the general Basil Vatatzes, who was killed in battle in 1194, and his wife, a cousin of the Emperors Isaac II Angelos and Alexios III Angelos. John Doukas Vatatzes had two older brothers. The eldest was Isaac Doukas Vatatzes (1188-1261), while his younger brother died young. Through his marriage to Eudokia Angelina he fathered Theodora Doukaina Vatatzaina, who later married Michael VIII Palaiologos. The middle brother's name is unknown, but his daughter married the protovestiarios Alexios Raoul. A successful soldier from a military family, John was chosen in about 1216 by Emperor Theodore I Laskaris as the second husband for his daughter Irene Laskarina and as heir to the throne, following the death of her first husband, Andronikos Palaiologos. This arrangement excluded members of the Laskarid family from the succession, and when John III became emperor in December 1221, following Theodore I's death in November, he had to suppress opposition to his rule. The struggle ended with the Battle of Poimanenon in 1224, in which his opponents were defeated in spite of support from the Latin Empire of Constantinople. John III's victory led to territorial concessions by the Latin Empire in 1225, followed by John's incursion into Europe, where he seized Adrianople. John III's possession of Adrianople was terminated by Theodore Komnenos Doukas of Epirus and Thessalonica, who drove the Nicaean garrison out of Adrianople and annexed much of Thrace in 1227. The elimination of Theodore by Ivan Asen II of Bulgaria in 1230 put an end to the danger posed by Thessalonica, and John III made an alliance with Bulgaria against the Latin Empire. In 1235 this alliance resulted in the restoration of the Bulgarian patriarchate and the marriage between Elena of Bulgaria and Theodore II, respectively Ivan Asen II's daughter and John III's son. In that same year, the Bulgarians and Nicaeans campaigned against the Latin Empire, and in 1236 they attempted a siege of Constantinople. Subsequently, Ivan Asen II adopted an ambivalent policy, effectively becoming neutral, and leaving John III to his own devices. John III Vatatzes was greatly interested in the collection and copying