title: List of emperors of the Han dynasty
context: The Han dynasty was founded by the peasant rebel leader (Liu Bang), known posthumously as Emperor Gao (r. 202 –195 BC) or Gaodi. The longest reigning emperor of the dynasty was Emperor Wu (r. 141–87 BC), or Wudi, who reigned for 54 years. The dynasty was briefly interrupted by the Xin dynasty of the former regent Wang Mang, but he was overthrown in 23 AD and the Han dynasty was reestablished by Liu Xiu, known posthumously as Emperor Guangwu (r. 25–57 AD), or Guangwu Di.[2] The last Han emperor, Emperor Xian (r. 189–220 AD), was a puppet monarch of Chancellor Cao Cao (155–220 AD), who dominated the court and was made King of Wei.[3] In 220 AD, Cao's son Pi usurped the throne as Emperor Wen of Wei (r. 220–226 AD) and ended the Han dynasty.
question: Who was the first ruler of the Han dynasty?
answers: Emperor Gao