Theodore, or Theodoros (Θεόδωρος), I Laskaris (Λάσκαρις) was the first Emperor of Nikaia and a Byzantine and Eastern Roman emperor of the 13th century following the Sack of Konstadinoupolis. He was known for his attempts to reclaim territory from the Latins and won a crushing victory in the Battle of Adrianople. He was able to receive support from the displaced Byzantine people and seized the domain of those who dissented. His establishment of the Nikaian state allowed for the later reconquest of Konstadinoupolis.