How did the practice of awarding the 3 'stars' of the game originate?

From:

When Imperial Oil joined Hockey Night in Canada as its principal sponsor in 1936-37, one of the traditions it established on the program was the post-game ritual of choosing the three stars of the game.

After the featured game ended, the three stars would be announced and each player would skate out onto the ice separately to receive applause -- or boos, depending on where the game was played.

Though the custom initially started as a way for Imperial to promote its "Three Star" brand of gasoline, it was also a way for the NHL to get recognition for its best ambassadors, players like Maurice "The Rocket" Richard of the Canadiens and Johnny Bower of the Maple Leafs.

When Imperial Oil left HNIC as a sponsor in 1976, the tradition of choosing the three stars remained.

Choosing the three stars of the game is not exclusive to HNIC, however. Just about every level of hockey has adopted the format as a way to recognize the best players on the ice in games and tournaments.

One famous "Three Star" selection was on March 23, 1944, when Maurice Richard named the No. 1, No. 2 and No. 3 stars after scoring all five goals in the Canadiens 5-1 playoff win over the Maple Leafs.