The title "Stars who started in Porn" suggests that actors made pornographic films to advance their Hollywood careers. This interpretation is nonsense, because porn would destroy any chances of success.
Yes, Hollywood stars have posed for nude photos and some have made nude and pornographic films. However, mostly they have been very private home movies and private photos we hear about as rumors. Supposedly there is a photo of Marlon Brando sucking cock. He probably didn't want the photo taken, and he certainly didn't do it for money or to advance his film career.
Some minor celebrities have started in porn and progressed to celebrity status, famous for being famous.
I've given this a lot of thought because I am in show biz and I do have an extra large cock. On the internet I keep my nude stuff entirely separate from my show biz stuff, with different names. I have concluded that a large cock can help a show biz career, but the large cock cannot be used in show biz directly. EVERYBODY has always known Milton Berle had the biggest cock in show biz, but he never used it directly in his career. But we knew, and it helped him. If he had published nude photos, made jokes about his cock, etc. it would have destroyed him.