Sun Wukong has served as a staff in the heavenly court for some time, one is the Protector of the Horses, who is in charge of horses, and the other is Great Sage, who looks after the flat peach garden.
However, on his way to get scriptures, the celestial immortals still called him Great Sage.
The immortal status in the heavenly court is very high. Wukong is nothing in their eyes. What they respect about Wukong is that they are afraid of the mountains (endorsement) behind him.
The first mountain: the White Planet
The White Planet directly protects the monkey king. On the way to get the scriptures, the White Planet appears around Wukong more than once to help him clean up the trouble. Under the protection of the White Planet, no one in the heavenly court dares to attack Wukong again.
The second mountain: Lord Lao Zi
Lord Lao Zi’s preference for Wukong is well known in the three realms.
The third mountain: Guanyin
Guanyin opened the back door for Wukong. For example, she personally came to Wuzhuang Temple to help brother monkey solve the problem with Zhenyuanzi.
The fourth mountain: Tathagata
The Tathagata pressed Wukong at the foot of the five elements mountain to prevent the Jade Emperor from attacking him. In fact, when he was pressed at the foot of the mountain for the first time, Wukong still had a chance to escape. Unfortunately, he made too much noise.
Eventually, brother monkey found a position in Ling Mountain. Brother monkey should thank Tathagata.
With these big names protecting Wukong, the immortals didn’t dare to do something bad to Wukong. Therefore, Wukong has been treated well by the immortals in three realms. That’s why most of them politely called Wukong “Great Sage”.