are there any festivals related to him?
Yes - Ramlila
Hanuman
Hanuman is a central character in the annual Ramlila celebrations in India, and seasonal dramatic arts in southeast Asia, particularly in Thailand; and Bali and Java, Indonesia. Ramlila is a dramatic folk re-enactment of the life of Rama according to the ancient Hindu epic "Ramayana" or secondary literature based on it such as the "Ramcharitmanas". It particularly refers to the thousands of dramatic plays and dance events that are staged during the annual autumn festival of Navratri in India. Hanuman is featured in many parts of the folk-enacted play of the legendary war between Good and Evil, with the celebrations climaxing in the Dussehra (Dasara, Vijayadashami) night festivities where the giant grotesque effigies of Evil such as of demon Ravana are burnt, typically with fireworks.

who is monkey king in the ramayana who helps save sita Hanuman who is "trijata"? She is a rakshasi (demoness) in the "Ramayana" who is assigned the duty of guarding Sita who was kidnapped by king of Lanka Ravana. rijata is describe as a daughter of Vibhishana. does she have any other name? Yes - Punukay, Benyakai, Devi Seri Jali can you describe who is the monkey king mentioned earlier? A Hindu god and divine vanara companion of the god Rama. which epic is he a character of? Ramayana, Mahabharata how is he a part in buddhism? Hanuman appears with a Buddhist gloss in Tibetan and Khotanese versions of Ramayana.  In Chinese Buddhist texts, states Arthur Cotterall, myths mention the meeting of the Buddha with Hanuman, as well as Hanuman's great triumphs.
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Hanuman [SEP] Festivals and celebrations
Hanuman is a central character in the annual Ramlila celebrations in India, and seasonal dramatic arts in southeast Asia, particularly in Thailand; and Bali and Java, Indonesia. Ramlila is a dramatic folk re-enactment of the life of Rama according to the ancient Hindu epic "Ramayana" or secondary literature based on it such as the "Ramcharitmanas". It particularly refers to the thousands of dramatic plays and dance events that are staged during the annual autumn festival of Navratri in India. Hanuman is featured in many parts of the folk-enacted play of the legendary war between Good and Evil, with the celebrations climaxing in the Dussehra (Dasara, Vijayadashami) night festivities where the giant grotesque effigies of Evil such as of demon Ravana are burnt, typically with fireworks.