Roy Thomas, who co-created Ultron and The Vision back in the 1960s, opens up about his old boss and why he tried not to create too many characters for Marvel: "I knew I wouldn't own any of it."

Stan Lee is the face of the Marvel Universe, but its summer crown jewel wouldn't exist without Roy Thomas.

Thomas and artist John Buscema created key characters featured in Avengers: Age of Ultron, including the titular killer robot, played by James Spader, and the breakout android The Vision (Paul Bettany). He succeeded Lee as Marvel editor in chief and also held key roles at rival DC Comics.

But in 1965, Thomas was just a 20-something comic book superfan from Missouri who walked into Lee's office looking for a job. He was already working as an assistant at DC, where he was miserable. Lee hired him on the spot. It was a good hire. Thomas went on to co-create Ultron and The Vision in the pages of Avengers in 1968 and also created a number of Marvel mainstays, including Adamantium (you are welcome, Hugh Jackman), Iron Fist (coming to Netflix soon) and Yellow Jacket (the villain played by Corey Stoll in the upcoming Ant-Man).

So it's only appropriate that director Joss Whedon put a Thomas Easter egg in Age of Ultron. During a dream-like sequence, Captain America (Chris Evans) sees a USO event in which the band is called the Roy Thomas Players.

"It's a nice touch," Thomas tells The Hollywood Reporter. "It's the closet I'll come to a cameo like Stan does."

In a conversation with THR, Thomas discusses the development of the characters, days of slaving away at Marvel in the '60s and why he didn't try to invent more characters (if he could help it).

Where did the idea for Ultron come from?

I never considered myself very good at making up names. Some of the first creatures I made up fighting The Avengers were part of a group called the Ultroids. I've always liked that tron ending. I had recently made up something called a psychlotron [a brainwashing device]. So I liked that tron ending, and Ultron just came as a good name.

Did you have a sense he would become so popular?

No. I was just looking for something to be the robot. He always had a smile on his face in the comic. I got the idea of his look from a Captain Video comic book from 1951. I must have showed it to the artist, John Buscema, otherwise I don't think he would have drawn the robot to look like that. It isn't the same face, but it had the same kind of malicious smile I wanted. That robot's name was Makino, who was a just in a one-shot story in Captain Video No. 3. But he was really formidable. He wanted to take over the Earth and obliterate humanity. I liked the tone of it, and that became the inspiration for Ultron.

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For The Vision, you wanted to bring back an old character of the same name, but Stan Lee said no.

I said, "What if I brought back The Vision from the old comics?" He said, "Naw, just do an android." I never asked him why. He didn't care what I did as long as it was an android, so I made up an android and called him The Vision, and he looked a lot like the old one. John Buscema added this great artistic touch, this little jewel on his forehead. I think in the movies, they are making it related to those gems of Thanos they're going to use in the next two movies, if I'm not mistaken.

What were your influences for The Vision?

I was influenced a little bit by Mr. Spock, though I didn't see any of that [Star Trek] much on TV. I used to hear it on the TV in the next room when I was playing poker on Friday nights. Also — a comic book writer who became a friend of mine in later years, Otto Binder — back in 1939 or '40, he had written the original title of the story "I, Robot," about a robot with human intelligence and feelings named Adam. That was one of the first sympathetic robot stories.

What was Stan's reaction to The Vision?

He liked it, but Stan hated the color of The Vision. "Why'd you make him red? Red's not a good color!" I didn't want to make him green like The Hulk or Blue like the Atlanteans. I suppose I could have made him white, but the paper we printed on was so poor, that you would have been able to see the other side, so we didn't make things white that we didn't have to. I don't think he ever thought The Vision was a really strong name. It seems a little wimpy, but I felt Vision — it really means like a ghost or a mirage or an image.

What was the atmosphere around the office at this time?

Being the associate editor, except for the broad strokes, I never had to get any approval from Stan. If I was going to make up a new major character, or kill someone off in a definitive way, I'd talk to Stan for a minute. We had a conversation about a new Avenger that couldn't have been more than a three or four minute conversation. Stan didn't approve the plots. He figured he could always hit me over the head if I did something wrong. He didn't have time to read plots. So we were just on our own.

Were you overworked?

Yeah. Stan would just load it on me. Luckily I had a deal, like he did at that time, where he allowed me to come into the office just two or three days a week. He wanted me the same days he was there. The other days, over the weekends, I was always writing. I was writing three or four comics a month at that stage, in addition to my editorial work.

You also created Adamantium, which is what Ultron is made out of — and is also used for Wolverine's claws.

That was in the second Ultron story. I was working with the artist Barry Smith. I wanted the story to deal with the hardest metal imaginable, and I was looking for a good name. In a particular English translation of the Greek tragedy Prometheus Bound, on the first page they had the adjective adamantine. It looked so good to me — it was just a slight switch there from adamantine as an adjective to adamantium as a noun. I'm always hoping that someday someone will discover a super hard mineral and name it adamantium. Then I will feel like my life and career were justified.

What other familiar phrases did you coin?

On Agents of SHIELD, they use this thing I called a Quinjet. They had these planes called twinjets, which meant a private jet with two engines. I thought Quinjet would be nice because it had five engines.

You've said you actually didn't want to create too many things for Marvel. Why was that?

I knew I wouldn't own any of it. I accepted the work for hire, and as a result I didn't want to create characters that much because I knew I would get resentful if they ever made movies and TV shows and merchandising out of it that I didn't get money and credit for. I was never going to sue over it or anything like that, I just knew what I was doing when I did it, and I wasn't going to claim otherwise later. Even if you don't try, you have to make up a few heroes here and there, and you have to make up villains. You can't keep using the same characters all the time.