The Latin emperor captured after the Battle of Adrianople in 1205 was Baldwin I. He had become the first emperor of the Latin Empire after the Fourth Crusade captured Constantinople and displaced the Byzantine government.
Baldwin led a Latin army into Thrace after Byzantine resistance broke out around Adrianople. The city had rebelled against Latin rule and received support from Kaloyan, the ruler of Bulgaria. On 14 April 1205, Bulgarian, Cuman, and Vlach forces lured the heavily armed Latin cavalry into an ambush outside the city.
The Crusaders’ pursuit carried them into prepared obstacles and an encirclement. Count Louis I of Blois was killed, much of the Latin army was destroyed, and Baldwin was taken prisoner. He was transported to the Bulgarian capital, Tarnovo, where he was imprisoned. His brother Henry assumed the regency and later succeeded him as Latin emperor.
Baldwin’s fate became uncertain to Latin subjects for a time, but he died in Bulgarian captivity later in 1205. Stories that his skull was made into a drinking cup are associated with later accounts, yet historians have found no firm evidence confirming that legend. The defeat severely weakened the young Latin Empire.