My Dad. I had been exposed to their music for a while but it was when I put the Best of 1980-1990 into the CD player for the first time that I really started to discover U2.
For me, it was seeing the video for NYD on TV in early 1983.
I tought playing the guitar, while wearing gloves in -20C, was sooo cool. I was already familiar with the Clash, the Police and Simple Minds, mostly from TV, but U2 were even better.
I didn't know anybody else interested in U2 until the release of JT.