J.G. Thirlwell (1960- ) is an Australian composer, experimental musician and record producer.

Since 1981, Thirlwell has released a long series of solo recordings under the pseudonymous band name Foetus (among the many, many other aliases he’s used). In addition to these, Thirlwell often lends his talents to other artists' recordings (often under some of the same pseudonyms), including Nurse With Wound, Coil, Sonic Youth, The The, Orange Juice, Nick Cave and Lydia Lunch. Thirlwell is also an accomplished producer, helming the board for artists like Swans, Pantera, Faith No More, Nine Inch Nails and Zola Jesus.

Since 2000, Thirlwell’s primary concern has been classical composition. He’s written pieces for modern classical groups such as Bang on a Can and Kronos Quartet. Perhaps most famously, Thirlwell has also composed the scores for acclaimed adult cartoon comedies Archer (from season 7 on) and The Venture Bros.