One of the pains — and one of the pleasures — of theater performance is that it is never truly preserved. And even when it is recorded, the record tends to rob the electricity of the live event, particularly when a performance — say, Al Pacino’s in David Rabe’s 1972 Vietnam drama “The Basic Training of Pavlo Hummel” — connects so powerfully with audiences.

So it’s just as well that we have no real record of Pacino’s early stage work, allowing it to live on in legend, a legend further fueled by the phenomenon that his stage breakthroughs with Rabe and Israel Horovitz (“The Indian Wants the Bronx” in 1966) were followed by a rarely matched string of film performances that were uncompromised by Hollywood convention.

It required extraordinary conviction and a sturdy backbone for Pacino not to opt out for easy stardom after his unpredictable achievement as Michael Corleone in “The Godfather,” especially given that his astounding lead film debut as a boyish/wolfish addicted drug dealer in Jerry Schatzberg’s “The Panic in Needle Park” (1970) was more admired than seen, illustrating the harsh reality that great work can frequently go unnoticed (a factor that has long plagued Schatzberg, whom Pacino calls “a tremendous director”).

Theater’s strong grounding

If there’s a lesson in Pacino’s example for younger actors lured to the siren call of celebrity, it’s that a strong grounding in theater and performance of all kinds is the sturdiest insurance against making fatally wrong choices and for knowing what stories really matter.

Pacino’s case begins in earnest with his training at the Actors Studio, which by the actor’s time of the early to mid-’60s had already seen its headiest days when the name of Lee Strasberg was synonymous with an American style of emotionally raw and instinctive acting glibly and wrongly designated as “method.” (It’s a term, incidentally, that Pacino never uses himself.) At the time of the fledgling and oh-so-serious actor’s involvement in the studio, Strasberg himself was a tad frightened by Pacino’s determination to immerse himself in a role 24/7: “Darling,” Strasberg finally pleaded with him, “you have to let go sometime.”

But the other side of the coin of this seriousness, which the Studio ingrained in him, was the exceptionally eclectic range of playwrights and theater styles that he became attached to in the theater worlds of New York and Boston, a city where he eventually developed an intense cult following. There were few actors of his age group who played in such varied work — often relatively obscure — by William Saroyan (“Hello Out There”), August Strindberg (“The Creditors”), Clifford Odets (“Awake and Sing!”), Jean-Claude Van Itallie (“America, Hurrah”), Heathcote Williams (“The Local Stigmatic” ), Tennessee Williams “(Camino Real”) and Bertolt Brecht (“The Resistable Rise of Arturo Ui,” “The Jungle of the Cities”). And fewer still combined this lineup with an ongoing comedy act he frequently performed in Greenwich Village nightclubs.

The ubiquitous Bard

The name not mentioned above, though, is the name most important to Pacino — yes, even more important than Francis Ford Coppola, whose chutzpah and insistence on sticking with Pacino in “The Godfather” is perhaps that filmmaker’s most sublime and prescient artistic and career decision, or manager-agent-producer Marty Bregman, who personally guided Pacino toward all of his early major film roles, from “Needle Park” to Schatzberg’s hugely underrated and misunderstood “Scarecrow,” to “Godfather II” and two mid-’70s collaborations with director Sidney Lumet, “Serpico” and “Dog Day Afternoon.” That would be William Shakespeare, who is typically the writer whom aspiring American stage actors will flirt with, and even become involved with, and then, like a lover who loses the intial thrill, drifts away from.

Pacino’s case reverses this trend: He didn’t do his first produced Shakespeare (“Richard III”) until 1972, first at Boston’s Home for Theater Company and then in New York. He then stepped up the pace, regularly revisiting and reconsidering Shakespeare ever since.

His devotion to Shakespeare is unrestricted by medium and by choice of play, and in this way, Pacino is the only major American actor-director working onstage and in cinema since Orson Welles to explore and struggle with the notion of making the Bard a living and engaging writer to U.S. audiences. Welles had the additional media of radio and audio recordings, and it seems unlikely that Pacino will ever direct Shakespeare on film in the protean fashion that Welles managed with “Macbeth,” “Othello” and “Chimes at Midnight.”

But Pacino has a different talent for bringing the aroma and the sting of the street (he was born poor in the Bronx and lived in utter poverty as a struggling Gotham actor) to his humpbacked Richard in his eccentric filmmaking debut, the is-it-a-doc/is-it-a-drama “Looking for Richard,” or, most recently, as a deeply embittered and sympathetic Shylock in Michael Radford’s naturalistic film version of the Bard’s supreme problem play, “The Merchant of Venice.”

He summarizes his populist approach to Shakespeare in the newly published compilation “Al Pacino in Conversation With Lawrence Grobel,” as the essence of the actor’s quest to connect with the writer and, thus, to emotional truth: “Shakespeare is the writer most likely to touch us, because he speaks to the emotions and feelings that are in all of us, and he speaks to them in the grandest way. We feel enormous things, and Shakespeare, in his genius and incredible sense of the human phenomena, was able to reach through to us and touch those feelings. He encompasses the size of stuff we feel.”

Channeling Prince Hal

This is the key to understanding the deeply repressed well of emotions in the Corleone family’s outsider son, the one least likely to assume the Godfather throne. Pacino is referencing Shakespeare’s “Henry IV Parts 1 and 2” (another hit with a sequel), where the young prince, at first disconnected from his father’s court, becomes a king. Or why Pacino’s brilliant, half-cracked vagabonder in the poetically searing “Scarecrow” is close cousin to the clowns of “A Midsummer Night’s Dream.” Or how, particularly in the early films up to and including “Dog Day Afternoon,” and then later with Pacino’s explicitly Richardlike Tony Montana in “Scarface,” Shakespeare’s men of feelings large and small are the connective tissue that binds and inspires the actor.

“Looking for Richard” and “The Merchant of Venice” underline, like no other American movie star of his time, that Pacino is happily haunted by Shakespeare and shows no sign of wanting to let go. Put another way: He may be too late for his Hamlet, but not for his King Lear.