She was one of the best-looking actresses on the screen in the '60s, and she was an excellent actress; after her acting career stalled, she went to London to teach acting at the Lee Strasberg studio (which is perhaps how she got the part in Godfather II, which featured Strasberg). She spoke several languages, which allowed her to do non-embarrassing foreign accents, a big plus in an era when it was considered somehow inappropriate for the heroine in an American movie to have an American accent.
In 1965 she was one of a bunch of attractive young men and women selected by Howard Hawks to play important roles in his disastrous attempt at a "youth" movie, Red Line 7000; a few years later he admitted that of all the people he signed up for the film, the only ones who could actually act were Marianna Hill and another young actor named James Caan. Their scene together in front of a Pepsi-Cola machine (an early instance of blatant product placement in a movie) was one of the few scenes in the film that worked. But Caan went on to bigger things; Hill did not.
I don't want to sound like a broken record here, but you'd think that a spectacular-looking person with acting ability and screen presence to match James Caan would go on to get a few meaty roles. Instead Hill went on to that graveyard of attractive young '60s actresses' careers, an Elvis Presley movie, Paradise Hawaiian Style. (Which, incidentally, was directed by "Michael Moore," thus undoubtedly earning the current Michael Moore a lot of ribbing.) She also got supporting parts in some good movies, like Medium Cool. But with better opportunities, she could have and should have been a big star.
There's a fan page for Ms. Hill that gives some more information on her career, including the fact that she changed her last name from Schwarzkopf -- her cousin, Norman Schwarzkopf, had an interesting career in a different field. And it includes a collection of '60s articles on Ms. Hill, including some fairly candid remarks about Elvis:
"He's always competing with the leading ladies. He doesn't seem to want you to get serious with your work because he knows you're better trained than he. So he likes to break up all the time and throw the scene. He doesn't concentrate on what he's doing. He acts as though he cares, but he doesn't.
"Like his veneer of politeness," Marianna went on to explain. "Elvis is always going Yes, sir and No, sir, Yes ma'am and No, ma'am. He pretends to be humble, but I'm not sure he is. Underneath it all, there seems to be a lot of resentment and defensiveness and hostility.
"Elvis does have a bag of tricks. Even if they're old, though. He has this physical thing-- this jumpy kind of thing-- that's often mistaken for something great coming across on the screen. At first glance you might think that it's warmth or depth. But it's not. It's some sort of nervous tic which, I think, is a result of surpressing impulses and having them come out physically.
"His eyes are always darting about. Very quickly. That's why I think Elvis is much like an animal. He reminds me of a kitten.
"Elvis has changed his image a lot. Remember when he was younger and really wild? That was great! But then he calmed down and got very GI and supposedly became very mature.
"I loved him when he was wild and crazy. Now it's like he's sold out to the enemy. Personally, I think the Colonel made the decision.
Calling Elvis a sellout in a magazine in 1966, and blaming it on Colonel Parker, probably wasn't a good way to advance her career.