Virtually unknown to the public here, Bill Cavala, a onetime UC Berkeley professor and top aide to Speaker Willie Brown Jr., was for most of two decades the Democratic operative most indispensable to the party’s San Diego legislative hopes. Cavala was a combination of the old and new politics. When he visited San Diego in the years before smoking was banned in bars, Cavala, a hard-drinking five-pack-a-day man, held court in the hazy happy hour at Bully’s East, where a steady procession of politicos and attractive women would stop by his table. Cavala had an uncanny grasp of slicing and dicing voters into groups to which precisely calibrated mail pieces could be sent. He also created TV campaigns for generations of local Democrats, including the famous “trench coat and fedora” spot in 1996, portraying Assemblyman Howard Wayne — whose public-speaking skills were not his strong suit — as a silent gumshoe. Cavala, 66, died in Sacramento the day after Christmas.