Aspen is best known as the founder of Groove Tubes, and the author of The Tube Amp Book, although his influence on the pro audio industry goes well beyond that.
I did not know him well, but always enjoyed speaking with him at NAMM. He was extraordinarily knowledgeable about microphones, and about the industry. When I last spoke with him, which sadly for me was a couple years ago, he was excited to be building up his "Aspen's Place" studio. His enthusiasm for audio was inspirational, as was his business savvy. I will miss him.
Here's a nice interview and studio tour, from Warren Huart's channel on Youtube: