'Austin Powers' Villain -- Victim ID'd in Prison Murder

The prison inmate who was allegedly murdered by "Austin Powers" actor Joe Son has been identified ... and authorities tell us he was a convicted child molester.

The victim has been identified as 50-year-old Thomas Graham (pictured above) -- who had once been convicted for committing lewd and lascivious acts on a child under the age of 14.

At the time he was killed, Graham was serving a two-year sentence in Wasco State Prison for failing to properly register as a sex offender.

As TMZ previously reported, cops believe Graham's cellmate Joe Son -- who played shoe-throwing villain Random Task in the original "Austin Powers" movie -- killed Graham in their cell on October 10.

Son is currently in solitary confinement while prison officials investigate.