Sindarin was designed by J.R.R. Tolkien as the language of the Grey Elves.
In Tolkien’s mythology, Sindarin is primarily spoken by the Sindar, or Grey Elves, of Middle-earth. It becomes the everyday Elvish language of many Elves in the Third Age and is used by characters such as Legolas and Elrond.
Tolkien developed Sindarin with a sound and historical structure influenced strongly by Welsh. He created related forms and changes over the imagined history of the Elvish peoples, treating the language as part of a broader linguistic family rather than as a collection of isolated words.
Quenya is a different major Elvish language, associated especially with the High Elves and influenced by Finnish. Khuzdul is the secret language of the Dwarves, while Adûnaic is associated with Númenor.