Larry Sonsini isn’t a high-tech visionary, but the veteran lawyer is one of Silicon Valley’s most influential figures. So when he assured Hewlett-Packard executives about the legality of their boardroom spying probe, the opinion must have carried considerable weight.

Sonsini, 65, the common denominator in some of the region’s biggest success stories, served as HP’s outside counsel, a relationship that landed him in the middle of the scandal.