(CNN) -- Robert De Niro has always liked to keep a bit of himself hidden from view.
"I've never been one of those actors who has touted myself as a fascinating human being," he reportedly once said. "I had to decide early on whether I was to be an actor or a personality."
Of course, the modern celebrity-industrial complex being what it is, he didn't get much of a choice.
In hindsight, it's hard to remember a time when De Niro, who turns 70 on Saturday, wasn't Robert De Niro, with his movie star image -- brusque, intense, Italian, New Yorky -- front and center. (In real life, De Niro -- despite his name -- is a mix of ethnicities, including German, Dutch and Irish, though he identifies most closely with his Italian heritage.)
But that wasn't always the case. In the first two decades of his career, he generally disappeared into roles as smoothly and casually as putting on a new suit.
You know them all, of course. The brash, manic Johnny Boy in "Mean Streets," the first of his many Martin Scorsese collaborations. The ailing, slow-witted catcher in "Bang the Drum Slowly." "Godfather II's" young Vito Corleone. "Taxi Driver's" Travis Bickle.
Jake LaMotta ("Raging Bull"), Rupert Pupkin ("The King of Comedy"), Al Capone ("The Untouchables"), Jimmy Conway ("Goodfellas") -- all chips of a multifaceted, diamond-bright talent. Oscar-winning, too: He took home the statue for 1974's "The Godfather: Part II" and 1980's "Raging Bull" and has been nominated five other times.
Those early characters often had something in common. Some were gangsters. Some had hair-trigger tempers. ("You talkin' to me?") There were often hints of hardscrabble lives aching for success, even in cases where they'd achieved it. (Behind the eyes of De Niro's Corleone, long after he starts wearing tailored clothes, are the haunted memories of tenement flats and Ellis Island.)
Still, there was always a sense of mystery. The 5-foot-9 actor had that mesmerizing ability to seem taller or shorter, depending on the role. He famously plowed himself into the Method, gaining and losing weight for "Raging Bull," driving a cab for "Taxi Driver" and learning saxophone for "New York, New York." He kept viewers off balance with occasional comic turns, whether it was as a cheerful repairman in "Brazil" or the exasperated bounty hunter in "Midnight Run."
It's no wonder Bananarama had a song called "Robert De Niro's Waiting," in which they fantasized about escaping with this enigmatic leading man, "talking Italian."
But, more recently, he has been Robert De Niro, the image taking the lead. Given his obvious acting abilities, sometimes it has gotten a little wearying. Why is Robert De Niro in "Showtime" and "15 Minutes"? Who talked Robert De Niro into "The Fan," "The Score" and "Righteous Kill"? Can't he work with Scorsese again?
What happened to the mystery?
Besides, the actor still gets his turns. He was a shambling spin doctor in "Wag the Dog," the creature in "Mary Shelley's Frankenstein," Fearless Leader in "The Adventures of Rocky and Bullwinkle," a parodistic don in "Analyze This" and "Analyze That," and the ramrod ex-CIA agent in the "Fockers" series.
He has even started showing a little more of himself. He broke down while discussing last year's "Silver Linings Playbook" on Katie Couric's talk show.
And whether Robert De Niro or Robert De Niro, he's been a steady presence. The guy's always working: more than 80 films since 1968, with seven this year alone -- including "American Hustle" with director David O. Russell, who directed De Niro's Oscar-nominated performance in "Playbook."
He promises more to come. After all, he's only 70.
"I might like to do things that are more retiring," he reflected in 2011. "But not retire. As long as I'm enjoying what I'm doing, why retire?"
Why, indeed? Birthdays are full of surprises.