Megadeth bassist David Ellefson spoke in a recent event called Musicians Institute and explained his first met with Dave Mustaine. He said (transcriped by Ultimate-Guitar):

“Well, it turns out there was a blonde-haired guy walking around with the complex, I go up, knock on his door, it turns out of he’s right up above us. He happens to be what appears to be a budding young rock star by the name of Dave Mustaine. And he had just gotten released from this brand-new group I hadn’t heard of yet called Metallica.

Metallica was was from Los Angeles, they had relocated up to San Francisco to acquire this bass player named Cliff Burton, and in so doing essentially planted themselves at where the whole Bay Area thrash scene started at.

And so Dave and I – we meet, we start chatting, we jam a little bit. One of the very first songs he wrote coming home from his stint with Metallica was a song called ‘Megadeth,’ which was later retitled to ‘Set the World Afire’ – it didn’t make it on a record until our third album [1988’s ‘So Far, So Good… So What!’]. But some of the earliest songs like ‘Killing Is My Business’ and ‘Peace Sells’ were songs that he was working on. He was very charismatic in his writing and quite honestly, Dave was the first rockstar that I met when I moved here.

I mean, you could touch tell sitting in the room with him this guy was the real deal. There were a lot of people walking down the boulevard that looked like Vince Neil, a lot of people that looked like David Lee Roth, but Dave was the real deal. And by way of the two of us both being named Dave, our love for heavy metal – I’m kind of like the Minnesota nice kid from the farm and I meet Dave who’s a street kid from California – we formed Megadeth. So that happened as a result of the Musicians Institute.”

Click here to entire speech via Youtube.