Is the Chinese term "Rulai Fo" identical to Sākyamuni or is he somebody else?
如来佛是不是释迦牟尼？还是另一人？

"Rulai" was translated from the Sanskrit word "Tathāgata". "Ru" means "suchness" (tathatā), or "according to the reality" (Yathābhūta?), i.e. the ultimate reality of all dhammas, while "lai" means "come". "Rulai" (Tathāgata) is interpreted in the Buddhist scriptures as "coming by the path of Tathāgata" or "coming according to the reality". Tathāgata is a general term and another name for "the Buddha". Thus Gotama Buddha can be called Gotama Tathāgata, and Amita Buddha can be called Amita Tathāgata.
“如来”这个名词是从梵语Tathāgata译出来的。“如”字就是“真如”（tathatā），即一切法（事物）的真实状况，它又包含“如实”（Yathābhūta?）的意义。佛经对“如来”的解释是：“乘真如之道而来”，又说“如实而来”。“如来”是一个通用名词，它是“佛陀”的异名。如释迦牟尼佛，可以称释迦牟尼如来；阿弥陀佛，可以称阿弥陀如来。