Five years ago, Larry Klayman was an obscure international trade attorney, sanctioned at one point by a federal judge for making a frivolous legal argument about a filing deadline he had blown.

Critics say he’s still being frivolous. But today, Mr. Klayman is obscure no more. The founder and well-paid leader of Judicial Watch Inc., a 30-person, 10-attorney public interest group, he heads a self-proclaimed anti-corruption gadfly industry.