is he mentioned in any other texts or scriptures?
Yes - Jain texts such as 'Uttarapurana' and 'Anjana-Pavananjaya'; The Sikh texts such as 'Hanuman Natak'; the Thai "Ramakien."
Hanuman
There are major differences from the Hindu text : Hanuman is a supernatural being in Jain texts, (Rama is a pious Jaina who never kills anyone, and it is Lakshamana who kills Ravana.) Hanuman becomes a supporter of Rama after meeting him and learning about Sita's kidnapping by Ravana. He goes to Lanka on Rama's behalf, but is unable to convince Ravana to give up Sita. Ultimately, he joins Rama in the war against Ravana and performs several heroic deeds.
Later Jain texts, such as "Uttarapurana" (9th century CE) by Gunabhadra and "Anjana-Pavananjaya" (12th century CE), tell the same story.
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. are there any festivals related to him? Yes - Ramlila did he have a family? UNANSWERABLE are there any movies made on his story? Yes - Bajrangbali, a 2005 animated film 'Hanuman'
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Hanuman [SEP] Jainism
"Paumacariya" (also known as "Pauma Chariu" or "Padmacharit"), the Jain version of Ramayana written by Vimalasuri, mentions Hanuman not as a divine monkey, but as a Vidyadhara (a supernatural being, demigod in Jain cosmology). He is the son of Pavangati (wind deity) and Anjana Sundari. Anjana gives birth to Hanuman in a forest cave, after being banished by her in-laws. Her maternal uncle rescues her from the forest; while boarding his vimana, Anjana accidentally drops her baby on a rock. However, the baby remains uninjured while the rock is shattered. The baby is raised in Hanuruha. There are major differences from the Hindu text : Hanuman is a supernatural being in Jain texts, (Rama is a pious Jaina who never kills anyone, and it is Lakshamana who kills Ravana.) Hanuman becomes a supporter of Rama after meeting him and learning about Sita's kidnapping by Ravana.