If Batman and the X-Men get prequels, why not Hunter S. Thompson?

He was certainly a superhero of a kind, just one whose powers mainly consisted of consuming copious amounts of alcohol while still, somehow, churning out wildly colorful, raging dispatches from the road.

“The Rum Diary” is based on Thompson’s heavily autobiographical novel by the same name, which he wrote as a 22-year-old in the early 1960s after a stint as a newspaper reporter in San Juan, Puerto Rico. It wasn’t published until 1998. Since then, Thompson’s friend Johnny Depp (who played Thompson in “Fear and Loathing in Las Vegas”) has been trying to adapt “The Rum Diary” to the screen.

“The Rum Diary” is essentially a portrait of the Duke as a young journalist. The stand-in for Thompson, the young novelist-reporter Paul Kemp (Depp), is trying to find his way and his writing voice: It’s the birth of Gonzo.

Criminally exaggerated resume in hand, Kemp has gone to Puerto Rico to try his hand as a reporter. He lands a job at the San Juan Star, whose editor in chief, Lotterman (the excellent Richard Jenkins), is at his wit’s end running a failing, diminishing daily.

Kemp is befriended by staff photographer Sala (Michael Rispoli), a burly, genial newsman who is nevertheless not once seen with a camera in hand. Kemp moves into Sala’s dilapidated dump of an apartment, which he shares with crime reporter Moberg (Giovanni Ribisi).

Kemp catches the attention of American businessman Sanderson (Aaron Eckhart), a smooth manipulator who is trying to push through an enormous development of a nearby, pristine island that’s pushing locals out in favor of American investors. Sanderson recruits Kemp to spin the development favorably in the Star.

A combative atmosphere between poor locals and rich Americans hangs in the air.

Sanderson’s slick, wealthy appeal is tempting to Kemp, who isn’t finding the constricting Star to be an especially noble pursuit, either. Even more alluring is Sanderson’s beautiful fiancée Chenault, played by Amber Heard. Kemp immediately falls for her and it’s no wonder: Heard is a stunning presence.

This builds slowly for Kemp into a moral crisis and, finally, an artistic tipping-point. “I don’t know how to write like me,” he says, but by the end of the film, it’s clear that Kemp/Thompson has found his legs. The guiding principle is a furious distrust of authority, and a key ingredient is hallucinogens.

You might expect a tribute such as this to be sycophantic, but director Bruce Robinson keeps a realistic tone.

Depp, at this point, would seem to not be aging. This more low-key performance as a Thompson alter-ego feels truer than the manic derangement of “Fear and Loathing,” but the role is also lacking yearning and real energy.

Thompson went on to find his voice, but “The Rum Diary,” entertaining and well-intended, comes just shy of discovering its own.