You may recall that in Doom and Doom 2, multiplayer matches took place in standard campaign maps. In other words, deathmatch had no maps designed especially for PvP skirmishes. It seems unthinkable now, because nowadays multiplayer maps are a fine art of their own (though plenty of level creators ended up making special deathmatch maps for Doom anyway).
With Quake, id Software started adding multiplayer maps of their own, and in a recent interview with PCGamesN, Tim Willits made the claim that it was his idea. Explaining how he wanted to use remaining map fragments from single-player levels to adapt for multiplayer, Willits claimed his idea was roundly mocked.
"They [John Romero and John Carmack] both said that was the stupidest idea they'd ever heard. Why would you make a map you only play multiplayer when you can play multiplayer in single-player maps? So I said 'No, no, no, let me see what I can do.' And that's how multiplayer maps were started. True story."
But is it true? Apparently not, according to other id Software veterans including Romero, Tom Hall and American McGee. The former wrote a lengthy blogpost on the matter, specifically denying the exchange between Willits, himself and Carmack ever happened.
"This never happened (Carmack verified this to ShackNews)," Romero writes. "In fact, we had been playing multiplayer-only maps in DOOM for years already. There had been hundreds of maps that the DOOM mapping community had made only for deathmatch by that time. DWANGO was a multiplayer-only service that had many multiplayer-only maps that are legendary today.
"American McGee even released a multiplayer-only map in November 1994 named IDMAP01. The incredible DOOM community invented the idea of designing maps only for multiplayer mode, and they deserve the credit. The game owes so much to them."
It's worth reading all of Romero's post for the nitty-gritty, where he also discredits Willits' claim that he had designed the first episode of Quake (it was a collaboration, with Willits designing less than half of the maps). He also points out that other FPS games, such as Rise of the Triad, had featured bundled multiplayer-only maps before Quake did.
Whatever the case, American McGee denied Willits claims on Twitter, and Carmack confirmed with ShackNews that he doesn't remember the conversation happening. We'll update this story when (or if) Willits responds.