- Actor Allusion: English dub Roger's first lines in the episode "Leviathan"? "I'd say you have the wrong guy; I'm not exactly a bounty hunter."
- Adored by the Network: In terms of anime that [adult swim] actually likes, it ranks up there with Cowboy Bebop and FLCL. Not only did they co-produce the second season (thus granting [adult swim] permanent airing rights to it), but they've aired it enough times to make back the season's budget several times over. On the other hand, the first season hasn't aired since back in the early 2000s, note though this can be chalked up to the show falling into limbo after Bandai Entertaiment closing and [adult swim] barely having a relationship with Sentai Filmworks after they got the rights.
- Anime First: Anime -> Manga -> Second season. As a result, some ideas from the (considerably darker) manga end up in the second season. The second season was then followed up by more Manga (unreleased in the US), with the purpose of tying up the manga continuity with the previously aired season.
- Keep Circulating The Tapes - Rescued: The rights to Big O were left hanging when Bandai Entertainment halted DVD production. Fortunately, Sunrise started auctioning their Bandai-owned shows to other distributors. As noted on the main page, Big O ended up in the hands of Sentai Filmworks. (Season 2 is Blu-ray exclusive due to [adult swim] participating in its production and thus having perpetual US broadcasting rights.)
- Name's the Same: Roger Smith shares his name with the multi-persona alien from American Dad! plus Sonic the Hedgehog's voice actor Roger Craig Smith.
- No Export for You:
- The second season has seen no release in European territories, and probably never will since Beez Entertainment has gone the route of its parent company and stopped distributing anime titles.
- Lost Memory the manga released after season 2, has never been licensed in English.
- Several short stories were cut from Viz' release of the original manga and remain unprinted in English.
- The Other Darrin: In the English dub of Season 2, Alan Oppenheimer replaced Milton James as the voice of Norman.
- Screwed by the Network: It is widely believed that the reason the series has such a Gainax Ending is because Adult Swim told Sunrise that a third season was very likely. Sunrise decided to make Season 2's ending more ambiguous, expecting to have another season to explain things. Despite season 2 breaking even its budget, Adult Swim decided to focus exclusively on comedies, and a third season was never funded. This isn't helped by the fact that the second season aired inconsistently. However, in a 2013 interview with CHO Japan, series creator Kazuyoshi Katayama stated that Cartoon Network had two stipulations when developing season two. One being more action, and two being to reveal the mystery of the series. Katayama had intended from the beginning to never reveal anything, and wanted to leave the series open ended and without a conclusion. This was because he wanted The Big O to feel like a classic adventure anthology series, where the viewer could start and end with any episode, with the overall mystery and quirks being the bizarre window dressings of the setting. He did however compromise with the network on this, resulting in the strange and inconclusive finale that answered a number of questions but opened even more.
- The Wiki Rule: Here.
- The series has been featured in Super Robot Wars, first in Destiny, and then more famously in the Z trilogy. The former played Roger fairly straight, while the latter threw in some Character Exaggeration and gave him his trademark verbosity and wit for his battle quotes.
Trivia / The Big O