Toto Bassist Mike Porcaro Dead -- Dies at 59 From ALS

Toto bassist Mike Porcaro died early this morning after a long battle with ALS ... TMZ has learned.

Porcaro's brother and band mate Steve posted on Facebook that Mike was surrounded by family at home and passed away peacefully in his sleep at 12:04 AM.

Mike joined the band Toto in 1983 alongside his brothers Steve and Jeff, but retired in 2007 due to ALS. Mike played bass on some of the bands biggest hits, including ... "Rosanna," "Africa," and "I Won't Hold You Back."

Porcaro was 59.