After the return to Ayodhya from Lanka, Rama blessed Hanuman to become the Brahma in the future.
Every Brahma has a lifespan of 100 years. After the completion of 100 years, Brahma leaves his soul and merges in Srimaha Vishnu. Then again a new Brahma will be born. The present Brahma has completed 51 years of life his life so far (the place where Brahma lives is called Brahmaloka and the time in brahmaloka is different from Earth’s time). After him, Hanuman will become the 9th Brahma for serving Rama and Sita.
Adventures of Hanuman:
Hanuman helped Rama and Sita a lot. In fact, without hanuman’s help, Rama could not find Sita and could not kill Ravana. Hanuman crossed the mighty ocean by flying above it in the sky after facing many obstacles very easily. He then went to Lanka and met Sita and took a bracelet from her to give to Rama.
He then returned to Rama and informed about the location of Sita in Lanka by giving the bracelet. Hanuman helped in the construction of the bridge in the Indian ocean. He fought furiously and killed many rakshasas. During the war he went to the Himalayas and brought Sanjeevani when Lakshmana fell unconscious and helped Rama immensely in the battle.
For this reason, Rama, upon the request of Sita for helping her in very difficult times, blessed Hanuman to become 9th Brahma in the future.