Yes, it looks like Mr. Mature could be it.
But one of the clues was confusing. He said something like "this actor started out weak in movies but got strong later". Okay I see that now as a reference to the movie "Samson and Delilah" (1949) but the way he put it, it sounded like the actor's career started out slow and he became a bigger star later. That was confusing because Mature started out in leading roles right away, and never needed to work his way up from bit parts or small roles.
And I still have no idea what was meant by that rather frightening statement about Terry Moore! (And not sure I want to know!)
Mature is correct...I agree that the early clues are vague, but the guys around here...well, you just can't give 'em too much info! Glad you got the 'weak/strong' inference Rich, but remember that his very 1st movie role was 10,000 yrs B.C....a grade C flick with no dialog and no name actors and the cheapest, fakest looking Allosaurus you ever saw in a movie until "Carnisaur'.
Terry Moore: The story goes that her studio boss (who ever ran the "Mighty Joe Young" movie lot) was couching Terry and she was his favorite at that time. He had info that Mature was hung like a mule, a dick of Berlean proportions and he used all his influence to put a stop to their dating. He need not have worried as Howard Hughs noticed her and she, like any other money grubbing starlet bolted from Victor post haste!
She related a story in a playboy interview that Hugh's promised to marry her (wink wink) So she met him on his Yacht and they sailed way out and the Captain "married" them...apparently Hughs did this quite a few times with starlets and had them stashed away all over the greater Los Angeles/Beverly Hills erea. But that is another story.
Thank you for playing "Who am I?"