Last week, fans discovered that the latest Pokémon games reference beloved Nintendo CEO Satoru Iwata, who died in 2015. The easter egg is touching, but it’s also kind of brief. Here’s the full story behind how Iwata saved Pokémon—and a closer look at why the man became so legendary.

Joe Merrick, proprietor of Pokémon site Serebii, shared images of a moment you can experience on Ultra Sun and Moon on Twitter earlier this month:

The exchange, which happens in the virtual Game Freak offices located in Ultra Sun and Moon’s Heahea City, can only be experienced if you happen to be holding a monster from the 3DS’ virtual console. (In this case, it’s Pokémon Silver.) If you meet those requirements, a character can say the following to you:

Boy, when we were told halfway through development to make Kanto, too...

I thought I might just expire on the spot! But I’m glad we made it that way.

When we were having trouble fitting all the data in for Gold and Silver, and we were really in a pinch, this amazing guy came along and made a program for us that solved all our problems. He went on to become the amazing president of a real big company soon after that, too.

That amazing guy is of course Iwata. Some of you may have heard this story already, but here it is for those of you who haven’t. Infamously, Pokémon Gold and Silver had a troubled development cycle. At the time, Game Freak, the developers, literally only had four programmers working on one of the biggest gaming franchises in the world. Naturally, the team wanted to make the games as ambitious as possible, which only added to the strain. Making things worse, the explosive popularity of the franchise also meant that Game Freak had to find a way to port the original Red and Green to America, something that threatened to push the release of Gold and Silver even further. The other big wrench in the mix was that, midway through development, Game Freak apparently had to add another region to the game—and they hadn’t planned for that. Actually, they had no idea how to make it all fit onto a Game Boy cartridge. It was a mess.

Enter Iwata, who helped devise a way for Game Freak to fit all the code onto the cartridge. Here’s how he recounts the tale, per an older Iwata Asks interview with Tsunekazu Ishihara of The Pokémon Company and Shigeki Morimoto from Game Freak:

Iwata: Although I wasn’t working for Nintendo at that stage, I ended up acting as a go-between for Nintendo and you for some reason. (laughs)

Ishihara: That’s right.

Iwata: At that time I wasn’t a Nintendo employee but was President of HAL Laboratory. At the same time, I was a board member at Creatures Inc. and I ended up being involved in analyzing the best way to localize the overseas versions of Pokémon Red and Pokémon Green. For that reason, I got hold of the source code for Pokémon Red and Pokémon Green and I would study that and suggest ways to localize it to the relevant department at Nintendo.

Ishihara: At the same time, Pokémon Stadium16 came out...

Iwata: Right. (laughs) You decided to release Pokémon Stadium for the Nintendo 64 and the first task was to analyze the Pokémon Red and Pokémon Green battle logic and send it over to Miyamoto-san and his team. You’d normally expect there to be a specification document, but there was nothing of the sort...

Morimoto: I’m so sorry! (laughs)

Iwata: No, no, it’s fine! (laughs) Studying the program for the Pokémon battle system was part of my job.

Morimoto: I created that battle program and it really took a long time to put together. But when I heard that Iwata-san had been able to port it over in about a week and that it was already working... Well, I thought: “What kind of company president is this!?”(laughs)

All: (laughter)

Morimoto: I was saying things like: “Is that guy a programmer? Or is he the President?”(laughs)

Iwata: To be blunt, at the time I was more of a programmer than I was a company president. (laughs)

Morimoto: (laughs) I was really taken aback that you could get to grips with such a complicated program in such a short space of time.

Ishihara: I remember thinking that there just weren’t that many people out there who would be able to read the entire Game Boy source code, which was by no means written in a highly-refined programming language, and grasp how everything connected with everything else. So Iwata-san, you analyzed the whole thing and reworked the code, decided on the way to localize Pokémon Red and Pokémon Green, got the battle system running on N64... I was surprised that you managed all of that...

Iwata: Well at that time, I felt that for the whole team at Nintendo, the biggest priority was not to do anything that would adversely influence the development of Pokémon Gold and Pokémon Silver. So I very naturally slotted in on the development side for Pokémon.

Morimoto: What’s more, there were the tools for compressing the Pokémon graphic code...

Iwata: Ah yes, the compression tools.

Morimoto: You were kind enough to create those tools.

Iwata: Yes. (laughs) Well, I had heard from Ishihara-san that you’d been rather concerned about it.

Morimoto: At that point, we got a little carried away and were making all sorts of demands, saying: “This part isn’t quite right - do you think you could fix it?” We had some nerve to be making those requests to a company president... (laughs)

Iwata: Well, I was willing to do whatever I could! (laughs)

Ishihara: It would have been a waste to just have you as President! (laughs)

All: (laughs)

Iwata: Being able to participate in that small way in Pokémon, I came to feel a real affinity for the software. In any case, while it was tough going, Pokémon Gold and Pokémon Silver were successfully released.

Ishihara: I remember that when Pokémon Gold and Pokémon Silver were released, I felt like a burden had finally been lifted from my shoulders. We’d had our sights set on the finish line of Pokémon Gold and Pokémon Silver for so long, and now that we’d finally completed the major series running right through from Pokémon Red and Pokémon Blue, I felt I could say to Tajiri-san: “I’ve fulfilled my duty!”

Just one of many examples of Iwata’s programming brilliance. What a guy.

Over at Serebii, you can read a catalog of the other trivia facts you can learn at the Game Freak offices. Did you know, for example, that the save sound is slightly different depending on what version of Pokémon you’re playing?