I've known Holger for ages. I've worked with him in product and as an analyst. He knows heaps about HRTECH, but he has the broadest knowledge of modern enterprise software than anyone I know. If I was to go on a quiz show about enterprise software I would want Holger as my phone a friend. Check out his research here.
He is a busy fellow on Twitter too. Like his colleague Ray Wang, he seems to be everywhere. Seriously though, if you ever want to cut through the vendor talk at a conference, just read Holger's twitter feed instead.
He also knows a lot about sport, so we may end up talking about Italian football or the Tour de France. Luckily for you he knows very little about cricket. He has a serious collection of running shoes and sneakers though.