Why is Ma Chao called "General Shenwei Tian"?

Ma Chao was born extraordinary. He is the second generation of the army and is naturally suitable for leading troops to fight. His father, Ma Teng, was a great warlord in the late Eastern Han Dynasty, and Liangzhou area was basically his territory. However, Marten is not very ambitious. Cao Cao gave him an official position, and he happily went to be an official, leaving the army to Ma Chao. But Ma Chao is different. Ma Chao dared to confront Cao Cao. He was very greedy for power. When Cao Cao became prime minister, he knew that Ma Chao was brave and good at fighting, and he had recruited Ma Chao many times. But Ma Chao did it. It would be great to be your own mountain king in Liangzhou, and it would be so humbled to work under others. He would rather be a chicken head than a sponsor.