Short answers, pulled from the story.
Constantine XI Palaiologos was the last Byzantine emperor, ruling from the 23rd of January 1449 until his death in battle on the 29th of May 1453 at the fall of Constantinople. He was the fourth son of Emperor Manuel II Palaiologos and Serbian noblewoman Helena Dragaš, and served as Despot of the Morea before becoming emperor.
Constantine XI died in battle during the Ottoman conquest of Constantinople on the 29th of May 1453. No reliable eyewitness accounts of his exact death survived, but most historical sources agree he died fighting in a last stand against Ottoman troops who broke through the city's walls.
Constantine XI considered the idea of abandoning Constantinople unthinkable. When Mehmed II offered him the Peloponnese and other provinces in exchange for a peaceful surrender, Constantine did not bother to reply. His entire reign had been shaped by an effort to defend what remained of the Byzantine Empire, and he chose to die in its defense.
Greek folklore holds that Constantine XI, known as the Marmaromenos Vasilias or Marble Emperor, did not actually die at the fall of Constantinople. According to the legend, an angel rescued him and turned him to marble, hiding him beneath the Golden Gate of Constantinople, where he awaits a call from God to be restored to life and reconquer the city.
Constantine XI supported the Union of the Eastern Orthodox and Catholic Churches, as did his predecessor John VIII. He viewed the union as a necessary price for securing western military aid against the Ottomans. Much of his populace, led by figures like Mark of Ephesus, opposed the union, and the controversy damaged public perception of his reign and complicated his efforts to attract western allies.
Most estimates place the total number of defenders between 6,000 and 8,500 soldiers, of whom 5,000 to 6,000 were Greeks, mostly untrained militia. An additional 1,000 Byzantine soldiers were kept as reserves inside the city. The Ottoman besieging army under Mehmed II may have numbered as many as 80,000 men, including about 5,000 elite janissaries.