Fire officials say the rescuer, who does not want to reveal his name, called 911 when he saw flames at the northeast-area residence overnight.
Battalion chief Allan Ball says he then put a ladder up to a second-storey window to allow the family to flee because the blaze had cut off their only other escape route at the back of the building.
The parents were carrying two small children down the ladder when crews arrived to quickly extinguish the flames that covered a wide area at the rear of the block.
At least two suites were damaged, one of them extensively.
Ball says it was a spectacular scene and the fact the rescuer wishes to remain anonymous speaks to the humility of Calgarians.
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