Alberto R. Cisneros (/sɪsˈnɛroʊs/; born September 23, 1973) is an American musician. He is the lead singer and bassist for stoner rock/doom metal bands Sleep and Om. He also was a member of Shrinebuilder and Asbestosdeath (the precursor to Sleep) and has put out nine releases as a solo artist.

Cisneros' earliest musical interests included an appreciation of Black Sabbath, in particular their first four albums.

In 1989 he formed the sludge metal band Asbestosdeath, taking up bass and vocal duties, with Chris Hakius on drums and Matt Pike and Tom Choi on guitar. Asbestosdeath released two EPs in 1990.

Following Choi's departure, Cisneros, Hakius and Pike recruited Justin Marler on guitar and renamed themselves Sleep. Cisneros jokingly called himself "Luke" in the early days of Sleep, in homage to "Luke's Wall", the title of the outro section of "War Pigs".

In 1991 Sleep released their first album, Volume One. They soon gained a devoted underground following in the doom metal scene.

In 1992 they released their next album, Sleep's Holy Mountain, an influential album in the early development of stoner metal.

Between 1995 and 1998, Sleep worked extensively on their next album, Dopesmoker, a single song lasting one hour. However, their record label at the time refused to release it, and in 1998 Sleep disbanded. An abridged form was released in 1999 under the title Jerusalem. Dopesmoker in its entirety was first officially released by Tee Pee Records on April 22, 2003.

On November 26, 2012, it was reported that Sleep had recently announced their own status as a "full, reunited band".