He is noted for his terms langue, or regularities and patterns in speech, and parole, or actual acts of speech.  
One of this man's theories was supported by the discovery that Hittite contained forms in which distinct reflexes of the laryngeals are recorded, and he explained how the vowel alternations of a came about in his first work, Memoir on the Original System of Vowels in the Indo-European Languages.  He is noted for his terms langue, or regularities and patterns in speech, and parole, or actual acts of speech.  The work he is most famous for is often considered the foundation for structural linguistics, though Charles Bally and Albert Sechehaye actually published it.  FTP name this Swiss linguist whose lecture notes and other materials were posthumously turned into the seminal Course in General Linguistics.
One of this man's theories was supported by the discovery that Hittite contained forms in which distinct reflexes of the laryngeals are recorded, and he explained how the vowel alternations of a came about in his first work, Memoir on the Original System of Vowels in the Indo-European Languages.  
Ferdinand de Saussure