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.

Son is already serving a life sentence for torturing a woman back in 1990.

The scumbag who played Random Task in "Austin Powers" has been isolated from other inmates at Wasco State Prison ... after allegedly murdering his cellmate Monday ... TMZ has learned.

Prison officials tell us ... Joe Son has been placed in administrative segregation for the time being, citing "safety reasons."

We're told Son was originally housed in an area reserved for new prisoners -- but after he was named a suspect in the death of his cellmate, Son will be on his own while prison officials investigate.

During his solitary confinement, Son will be allowed to enjoy 10 hours of yard time a week -- and he'll also have regular shower privileges.

As we previously reported, Son is already locked up on a life sentence ... for participating in the brutal rape and torture of a young woman back in 1990.