Leonardo DiCaprio’s portrayal of Jack Dawson in “Titanic” does not represent the actor’s best work. As a matter of fact, it wouldn’t even rank on a list of his top 10 performances. (“What’s Eating Gilbert Grape?,” “This Boy’s Life,” “The Departed,” “Romeo + Juliet” ... they all come first, don’t they?)

But his role as the loogey-hocking, Rose Dewitt Bukater-wooing, young man of steerage class was the one that turned the then-23-year-old into a star so big, he could be identified with just one word: Leo.

View Photo Gallery: With the 3-D version of “Titanic” set to arrive in theaters, the time is right to reflect on Leomania and other Official Teen Heartthrobs (henceforth known as OTH) of yesteryear.

With “Titanic” back in theaters in 3-D, let’s retrospectively analyze why 1997 Leo DiCaprio made young ladies so irrationally swoony that they actually believed this Celine Dion song was really, really good.

For the purposes of this discussion, we shall not comment on how DiCaprio has evolved as a heartthrob over time; via some good-natured teasing, Kate Winslet already took care of that for us.

Let’s think back to “Titanic”-era Leo — post- “Quick and the Dead” but pre-“Catch Me If You Can,” before Bundchen and Bar, prior to acquiring official status as spokesman for the Earth. We’ll call it DiCaprios’s Dreamboat Period.

View Photo Gallery: “Titanic” vaulted young Leonardo DiCaprio and Kate Winslet to superstardom. Take a look at the film’s cast 15 years ago and now, as the film is re-released in 3-D for the 100th anniversary of the disaster.

The former “Growing Pains” star had already earned his first Academy Award nomination (for the aforementioned “Gilbert Grape”) and established his pin-up boy charms, especially in “Romeo + Juliet,” before he made James Cameron’s ship-sinker.

In fact, Baz Luhrmann’s take on the Shakespearean tragedy teed him up perfectly for “Titanic,” in which he also played a Romeo of sorts, by which I mean a young man unafraid of authority, vaguely dangerous but totally adoring of his lady love, disliked by that lady love’s parents/mother and a romantic. Sketching a naked Rose is, as we all know, the “Titanic” equivalent of saying, “But hark, what light through yonder window breaks?”

In his early 20s, DiCaprio was handsome, but his features were soft and boyish. At the time, some women over the age of 30 had a hard time embracing him as a male lead because he looked so young. But for those closer in age to Leo, there was something about the way Jack Dawson’s totally-inappropriate-for-1912 bangs dipped his face, something about the way his mouth moved when he said “You jump, I jump,” something about the way he urged Rose to seize life — and by seize life, I mean avoid suicide, spit phlegm, blow off her fiance, throw back a few pints and do a little riverdancing, then have sex in the back of a car even though you’re on a super-expensive boat where there are clearly other options — that provoked primal urges.

DiCaprio was then, and still is, a magnetic presence onscreen; even though this is not his most nuanced performance, that much certainly comes across in “Titanic.” It’s the reason some people still make cheese-tastic YouTube montages like this one in his and Winslet’s honor.

But it’s not the only explanation for the fervor of Leomania.

Like any actor who stars in a film that becomes a global phenomenon, for a little while, DiCaprio was synonymous with his “Titanic” character. The mere sight of him conjured up all those things that Jack Dawson represented to so many sighing young girls and women: the promise of love that shakes us out of our routine and — this is the more important part — actually does last forever. Cornball stuff, but stuff that resonates, especially with teenagers.

“Love can touch us one time/and last for a lifetime,” Dion tells us in that treacly “Titanic” love theme. When you’re 15 and desperately in love with the boy who sits in front of you in geometry — the kid who inspires such desire in you that you spent three hours on Sunday night daydreaming about him while listening to Donna Lewis’s “I Love You, Always Forever” on repeat — that’s what you need to believe. This isn’t just temporary or right now; these feelings are real. They’re enduring. They’re like ... like ... like Jack and Rose in “Titanic.”

In other words, for a little while — until he grew up and and started earning Academy Award nominations for playing obsessive-compulsive billionaires and G-men — Leonardo DiCaprio was the face of young, heart-racing love, the kind that 14-year-olds hope to one day find or believe they’ve already found; the kind that their mothers are happy to be blissfully, wistfully reminded of; the kind that, when evoked in a sweeping three-hour love story that results in beautiful, baby-faced Leo (sob!) slipping into the sea, sells a hell of a lot of movie tickets.