Back in the mid-1980’s, Oliver Stone met with famed financier Carl Icahn about a movie he was writing called “Wall Street.” The meeting provided the director with much of the inspiration for the film’s villain Gordon Gekko. Stone speaks about the meeting in HBO’s documentary “Icahn: The Restless Billionaire,” debuting on Feb. 15. Along with Stone, the 100-minute docu features interviews with Icahn, his wife Gail and children Brett and Michelle.

Microsoft co-founder Bill Gates, and business journalists including Andrew Ross Sorkin (New York Times), Cara Lombardo (The Wall Street Journal) and Rana Foroohar (Financial Times) also help director Bruce David Klein unpack many of the octogenarian billionaire’s legendary business dealings. Corporate deals that include Icahn’s takeover of TWA in the 1980s, his 2013 high-profile investment in Apple, which provoked a stock rise of $17 billion dollars, his public battle with Bill Ackman over Herbalife that same year, and his role in the 1988 Texaco bankruptcy.

The docu also shines a human light on Icahn – a polarizing character who is widely known as ruthless corporate raider.

Variety spoke to Klein about convincing Icahn to be the subject of a docu, making complicated financial terminology understandable and why the director decided to leave the billionaire’s relationship with Donald Trump on the cutting room floor.

Why a film about Carl Icahn now?

People know that Carl is a multi-billionaire and that he’s successful and that he’s feared and that he is a great negotiator, but I wanted to explore what is it really about his unique makeup and his extreme complexity that allows him to surpass the best of the best in the financial world. In terms of why now? Certainly, the lion in winter is an interesting theme. What happens to somebody who is known for his explosive energy and restlessness and what happens to him when he’s in his mid-eighties?

You had access to not only Icahn but his family members. He allowed you into his house to film personal moments. How did you gain his trust?

Lots of, shall we say, hardy debate. Carl loves to debate and interestingly he’s not really a “my way or the highway” type of guy. He actually enjoys the back and forth. He enjoys long phone calls, long meetings, and he asks a million and one questions. From the beginning, he was fairly gung ho about telling the stories of business and very interested in the nuances of the deals, negotiations, and strategies. So, when I talked to him about that, he was definitely leaning in. When it came to capturing the personal aspects of his life, that took a little while for him to get comfortable with. He doesn’t really watch documentaries, so it was challenging to explain to him that people who watch documentaries are interested in the personal side of (the subject). They want to know what you are like every day when you kick back.

Did Icahn serve as a producer or have final cut?

No. He was not a producer. This is a hundred percent an HBO film. It’s an HBO-financed film. But he has seen the film.

And he didn’t ask you to take anything out?

No. I mean, I think he would’ve loved for me to delete some of the personal scenes that are a little more revealing, but those are obviously still in the film.

In the doc there is a lot of financial jargon that you unpack and make understandable for the layman. Was that a difficult part of the edit?

You could go so deep into every one of the financial deals that we cover in the film in terms of their financing and about how they put the deal together. But what I tried to do with each of Carl’s very complex deals is to take one or two essential moments in the deal that reveals Carl’s character. I worked hard to make sure the audience understood what the stakes were and what was at stake for Carl.

There is no mention of Icahn’ first wife, Liba Trejbal, or his relationship with Donald Trump. Icahn not only endorsed Trump in the 2016 Presidential election, he also agreed to serve as a special advisor to the former president on issues relating to regulatory reform. Why didn’t Icahn’s relationships with Trejbal and Trump make it into the doc?

The question is, in a two-hour film, what is relevant to understanding who Carl Icahn is? With his first wife — you know he’s been happily married for 20 plus years to Gail so that’s the relationship that seemed important. This is not really a biography of him. It’s more of a probing of someone’s philosophy. In terms of Trump, my feeling was after investigating it, his relationship to Trump was so tangential and really not important in his life to him. So, I didn’t really feel that there was much of a story there, quite frankly.

By leaving that out, some may say this film is a love letter to Carl Icahn. What would be your response?

I was really interested in Carl’s philosophies, and I think I show sides of his philosophies, both pro and con, so that audiences can make up their own minds about him.

“Icahn: The Restless Billionaire” debuts at 9 p.m. Feb. 15 on HBO.