This guy's real name is Adam Pearlman. I've known many crazy Jews, but converting to Islam and joining al Qaeda? This may be a new record.
Gadahn was born Adam Pearlman, the son of musician Phil Pearlman. Gadahn's family raised goats on a farm in Riverside County, California and butchered the goats in accordance with halal food requirements for sale to Muslim groceries. Gadahn's Jewish grandfather was a prominent surgeon named Pearlman but Gadahn's father converted to Christianity and changed his name to "Gadahn", derived from the name of the Biblical figure "Gideon". He was homeschooled until 15, when he moved in with his grandparents in Santa Ana, California. Gadahn was fond of heavy metal music and later briefly listened to fringe fundamentalist Christian radio stations before converting to Islam. In 1995, Gadahn posted an essay to the USC website describing his conversion, entitled "Becoming a Muslim".[2] According to his parents, Gadahn moved to Pakistan in 1998, where he married an Afghan refugee and maintained intermittent contact with his family.[3] http://www.usc.edu/dept/MSA/newmuslims/yahiye.html (USC Muslim Student Association website with Gadahn's writings)
I think only his father was Jewish, and I don't believe he himself was brought up as anything other than Cali New Ager. IIRC, he was in a goth phase before he joined AQ.
His grandfather was a Jew, changed his name to Gadahn and became a Christian, while his mother is a Catholic, and his father was an atheist/agnostic, who had a conversion to Christianity a few years before Adam Yo-Yo converted to Islam, because as he stated, most of the things in the Bible didn't make sense to him or sounded ridiculous.