how did Zheng He become an official in emperor Yongle's government?

Vivian, Zheng He's former name is Ma He. Ming armies attacked Yunnan in 1381. Ma He was captured by a Ming Dynasty general and brought back to Nanjing when he was 10 years old. Later, he was castrated and followed Zhu Di. Emperor Jianwen started to cope with regional princes by weakening their powers. Zhu Di rebelled agains him and finally defeated Emperor Jianwen. The war between then was called Jingnan Battle.

Ma he made great military achievement during the battle. Therefore, Zhu Di gave him a new surname Zheng and promoted him. After Zhu Di became the emperor, Zheng He became a high-ranked official in the government. He had seven voyages to the Western World from 1405 to 1433. Unfortunately, he died in 1433, during his seventh voyage.