Theodore I rose to power out of the wreckage of Byzantium following the Fourth Crusade of 1204. A son-in-law of Alexios III, Theodore fled Constantinople in 1203 and took refuge in Asia Minor at Nicaea. Given a respite from Latin attacks after the crusader defeat at the hands of Kalojan of Bulgaria in 1205, Theodore organized an empire in exile in northwestern Asia Minor. He was acclaimed emperor in 1205 and crowned at Nicaea in 1208. Theodore laid many of the foundations for Nicaea’s eventual rise to prominence over the other successor states by establishing institutions that they could not replicate. Most importantly, he attracted the patriarch Michael IV Autoreianos to his court. Although the Komnenoi in Trebizond and Theodore Komnenos Doukas in Thessaloniki would also claim the imperial title, only Nicaea replicated the situation as it had existed in Constantinople before 1204, with emperor and patriarch working side–by–side. Theodore also created a mint in Nicaea. Again both of his rivals, and the Latins in Constantinople, struck coins, but Theodore was the only claimant to Byzantium to strike a full range of coins, most importantly gold, just as the old emperors had done.
Theodore had mixed success on the battlefield. In 1211 he faced two invasions: first the Seljuk Sultan attacked Nicaean territory from the east, and then the Latin Emperor invaded from the north. Theodore defeated the Seljuks by killing the sultan in single combat, however he was then defeated by his Latin rival Henry of Hainault and was forced to make territorial concessions to the Empire of Constantinople. With peace in the West Theodore was able to attack the Empire of Trebizond, annexing its westernmost provinces in 1214. Nicaea continued to thrive, and when Theodore died in 1222, he left his empire to his son–in–law, John Vatatzes, who was ready to begin the laborious process of rebuilding Byzantium.
Theodore’s seal depicts his holy namesake St. Theodore Stratelates, a popular military saint, on the obverse and the emperor in his regalia holding a labarum on the reverse. Although he is known to history as Theodore Laskaris, his seals identify him as Theodore Komnenos Laskaris. This inscription shows Theodore continuing the trend started (on seals at least) by Alexios III of choosing the family name of one of the emperor's ancestors, and using it to gain prestige or a link with a former imperial dynasty.