Stanley Zax, chief executive of Zenith National Insurance Co., who built the Woodland Hills insurance carrier into a major national workers’ compensation insurer, is retiring next month.

The announcement came Tuesday from Zenith parent Fairfax Financial Holdings Ltd. of Toronto. Jack Miller, current Zenith chief operating office, will succeed Zax as chief executive on Jan. 1.

Zax, 74, joined Zenith Insurance as chairman in 1977 and became chief executive in 1978. At the time, Zenith sold workers’ compensation insurance to companies in Southern California; Zenith now does business in 45 states. Through the years, Zax emerged as an insurance industry spokesman on workers’ compensation policy.

Fairfax bought Zurich in 2010 in a cash transaction valued at $1.4 billion and then took the company private.