The veteran actor was 27 years old when he and then-wife Diana Dill welcomed Michael in 1944 and Kirk's film career kicked off shortly afterwards.
And Michael admits he was overwhelmed seeing his father working on such massive movies.
He tells Britain's The Guardian, "Kirk's career was constant, overwhelming - the guy didn't stop. Back then they were doing five movies a year. My father did 90-plus films. He was Spartacus!
"I always admired his tenacity and stamina but he was intimidating to me as a child. Like a lot of actors, he was consumed with ambition and his career."