Frieza is one of the strongest aliens in Dragon Ball Z. He enjoys invading other planets and is one of the best villains in the story.
The first appearance of this villain in Dragon Ball Z was built very successfully. Everyone is afraid to say his name, King Kai begs Goku not to get into a fight with him, Vegeta is scared at the thought of having to fight him. This fear has painted a complete portrait of the most powerful demon in the universe – Frieza.
Even though Frieza was defeated by Goku's group at least three times, he still tried to return to take revenge. In Dragon Ball Super, Frieza achieved a transformation that neutralized Goku and Vegeta with a single blow, two Saiyan warriors who were in Ultra Instinct and Ultimate Ego modes at the time.
The transformation that helps Frieza achieve this milestone is called Black Frieza, far superior to Golden Frieza in Dragon Ball Super.
This impressive power he achieved after 10 days of training in the Time Chamber (equivalent to 10 years in real time) located on another planet that we do not know about, in Universe 7 of Dragon Ball Super. In this way, we can think that Frieza is not afraid of any fight with any opponent.
However, Akira Toriyama revealed in an old interview that there are two unique warriors with whom the world conqueror never wants to compete.
According to an article by Sensa Cine, Akira Toriyama revealed that Frieza is afraid of facing the God of Destruction Beerus and Majin Buu.
The thing is, for Beerus, Frieza has some respect because he's a god so he can't defeat him by any means. The God of Destruction can destroy Frieza with just one finger.
In the case of Majin Buu, it was clear that his reputation had spread from the demon realm and information about his existence had reached King Cold (Frieza's father). Therefore, King Cold advised his son to never face Majin Buu in battle.