SEO ROI aka Gab Goldenberg is an advanced SEO consultant from Canada. He is widely known in the SEO industry and I follow him and his blog for a few years by now.
Gab has always been a great help and an inspiration. His early focus on ROI is by itself a sign of his skills. 4, 5 years ago when SEO was in for most people about PageRank, rankings and traffic he was already promoting hard core business metrics.