instruction: Given this paragraph, who was the President of Mexico during the seige of Bexar?
context: The siege of Béxar (or Béjar) was an early campaign of the Texas Revolution in which a volunteer Texian army defeated Mexican forces at San Antonio de Béxar (now San Antonio, Texas). Texians had become disillusioned with the Mexican government as President and General Antonio López de Santa Anna's tenure became increasingly dictatorial. In early October 1835, Texas settlers gathered in Gonzales to stop Mexican troops from reclaiming a small cannon. The resulting skirmish, known as the Battle of Gonzales, launched the Texas Revolution. Men continued to assemble in Gonzales and soon established the Texian Army. Despite a lack of military training, well-respected local leader General Stephen F. Austin was elected commander.
response: Based on this text, during the seige of Bexar Antonio Lopez de Santa Anna was the President of Mexico.