Billionaire investor Stephen Jarislowsky, a champion of corporate governance and former spy, has died at the age of 101.

Mr. Jarislowsky co-founded what became of one of the country’s largest asset management firms, Jarislowsky Fraser Ltd., after moving to Montreal in the 1950s.

Mr. Jarislowsky made his name as a pioneer advocate for shareholder rights, engaging in public battles with CEOs, family businesses and boards of directors.

He fought against deals put forward by Canadian corporate titans, including the Billes family behind Canadian Tire, Montreal’s powerful Bronfman clan, the corporate raider Conrad Black and auto parts magnate Frank Stronach.

Mr. Jarislowsky frequently and successfully pushed foreign companies attempting takeovers in Canada to improve their offers, with the quiet support of his money management peers.