What language is the Elvish language from "The Lord of the Rings" based on, and who created it?

Tolkien's love for languages began in his childhood when he learned Latin, French, and German. He later acquired knowledge in Old and Middle English, Old Norse, Welsh, and other European languages. It was his deep admiration for the Finnish language and the "Kalevala," a Finnish national epic, that inspired Tolkien to create Quenya. Sindarin, on the other hand, was derived from his love for the Welsh language and its poetic form. Tolkien continued to refine and expand his Elvish languages throughout his life, making them more complex and detailed.