One of the main reasons for the change in the Gundams’ design from their unusually intricate styling in season one to the more traditionally blocky types in season two was due to Sunrise complaining that the former were too difficult to animate.
Also, director Mizushima stated in an interview that the series was originally supposed to be set in Universal Century but Sunrise vetoed it, so the series was rewritten into a new 'verse, hence the similarities: Minovski particles = GN Particles; Newtypes = Innovators; Cyber Newtypes = Innovades, etc...
Gundam 00 as it was originally conceived wasn’t split into two seasons, with various events supposed to play out quite differently and at a different pace. Then Sunrise split the show into two 25 episode seasons...
His twin, meanwhile, became known as "Lockoff" (at least by the Japanese and Chinese fandom) as soon as he appeared in episode 9 of the first season, long before Lyle actually replaced the deceased Neil as Lockon Stratos. Eventually, "Lockon V2"/"Lockon 2.0" became popular, as well, was also nicknamed 'Lecharous Lyle' early on in Season 2 after his playful comments towards a clearly unamused Tieria Erde and stealing Feldt's first kiss (earning him a rather nasty slap for it).
The AEU's (alleged) ace Patrick Colasour is affectionately called "Team Patrick", for Pokémon's Terrible Trio and their shared habit of being quite soundly defeated and showing up again next episode anyway.
A more pragmatic example than most, Allelujah/Hallelujah is often shortened to "Al" and "Hal" by fans. Their temporary Split Personality Merge tends to be called "Doublelujah", for obvious reasons.
Setsuna F. Seiei, because of his past, is sometimes called "Jihad-kun". "SetLight", referring to the fact that both his English and Japanese voice actors provided their respective versions of Death Note's Light Yagami, is also popular. In Japan and China, he's apparently known as "Braindead".
The Japanese love to shorten things, so Graham becomes "Ham" and Alejandro becomes "Doro" (after the Japanese pronunciation).
Johann Trinity is nicknamed "Captain Hotpants" because of his wardrobe choice and his position as the leader of the Gundam Thrones
Even before his alias was revealed, fans were referring to Mr. Bushido as "Bushido Bob", thanks to his obvious Samurai stylings. His Japanese fan nickname, on the other hand, is HamMask, referencing his previous nickname before donning the mask.
The red-eyed, one-armed Exia from the start of season two is commonly known as "TerminExia".
The as-yet-unnamed black leader of the Earth Sphere Federation has been given the unofficial title of ""00bama"", a rather obvious reference to President Barack Obama.
The Innovators are sometimes referred to as "The Skittles Squad", for their odd hair colours.
Which is ironic, because some fans like to refer to Trans-Am Burst as "The Power of Skittles".
Col. Sergei Smirnov has HORDES of fanatically devoted Japanese fans who affectionately call him "Kuma-san" (Mr. Bear)note based on his In-Series Nickname, The Wild Bear of Russia. He gets the much-less-flattering Pedo-Bear from his western fanbase, thanks to his "relationship" with Soma. The neutral version of this is "Papa Bear".
Don't forget Rindt being nicknamed "Swiss Chocolate Man" because of his name...
The Seraphim Gundam is henceforth christened the "Gundam Lagann".
And "Shin Musha Flag" is now the nickname for Mr. Bushido’s new mobile suit(s), the Masurao and Susanowo.
The A-Laws' Captain Goodman is more often than not called "Captain Fat Ass", or alternatively "Captain KFC", for reasons that should be obvious.
The A-Laws are sometimes called A-LOLS, and less affectionately the A-Holes.
Throughout both English and Japanese speaking fanbases, Regene Regetta is the butt of many "NEET" jokes due to his supposedly lazy nature; fittingly, the Japanese have dubbed him as "The Royal NEET".
Chinese Girl Wang Liu Mei is widely known as "China Tits" or, less affectionately, "China Bitch".
Gundam Throne Drei is also been called "Dreivangelion", for its stunt in episode 15 of the first season.
And there's also "SoMarie", a portmanteau of Soma and Marie.
The 00 Gundam is known among fans as "Double Exia".
Marina Ismail is often called "Princess Poverty", and rules over the land of "Povertystan."
"Trans-GrahAm" - Whether Graham is using the Trans-Am system,
lternatively Trans-GARHam, on account of Graham's general hotbloodedness.
Being so hilariously obvious and memetic, the name (complete with cross out) was actually in one of the subs when the episode it first appeared in was translated.
By extension this also extends to his ultimately full of win quotes in SD Gundam G Generation Wars. where he is VERY notable for the aptly named "God Graham Finger." Also serves as a Crowning Moment of Awesome.
"Desu-Yellow" is a derisive one some fans have given Mileina Vashti because they can't stand her.
Quebeley Mark III - The Regnant due to its shape in Mobile Suit mode.
The army of Bring and Divine clones are known as both the "Red Ribbons Army" and "Bringivines".
Ribbons' mobile suit (Reborns Gundam) during the finale was actually jokingly called "Ribbons Cannon" by Tōru Furuya, Ribbons' seiyuu. Western fans generally just call it the GN Guncannon, while Asian fans call it GN Guntank.
Now also known as "GN Two-Face Hi-Nu Gundam", or just "GN Hi-Nu".
Same fans call the 00 Raiser "God Raiser" for various reasons.
"Bad Haro" for the purple, foul-mouthed Haro Nena Trinity kept inside the Throne Drei.
Was it mentioned that Setsuna F. Seiei was once a pony too? Setsuna's English voice actor Brad Swaile voiced Ace, Starlight's love interest in My Little Pony Tales.
Things got even cuter for Miyano. He later voiced the Deadpan Snarker government agent Keigo Tatewaki from the first Jewelpet series, who is pretty much an epitome of comedy and gags. Fans didn't expect Miyano to use the same personality as the Setsuna depicted in the two gag CD dramas in such a sugary series.
Relationship Voice Actor: Many seiyuus from Fullmetal Alchemist, another anime directed by Seiji Mizushima, reunite in 00. Namely, the voices of Edward Elric (Regene Regetta), Alphonse Elric (Nena Trinity), Maes Hughes (Ali al-Saachez), Scar (Bring Stability and Divine Nova), Riza Hawkeye (Shirin Bakhtiar), Jean Havoc (Alejandro Corner), Maria Ross (Revive Revival), Kain Fuery (Andrei Smirnov), Zolf Kimblee (Billy Katagiri), and Lt. Yoki (Aner Rindt).
In Fullmetal Alchemist: Brotherhood, many seiyuus from 00 replaced some of the originals, such as Roy Mustang (Lockon Stratos), Zolf Kimblee (H/Allelujah Haptism), Envy (Kati Mannequin), Vato Falman (Patrick Colasour), Barry the Chopper (Ian Vashti), and Greed (Graham Aker). Some of the seiyuus from the original anime that were also in 00 returned but voiced different characters, such as Billy Katagiri (the original Zolf Kimblee now Jean Havoc) and Andrei Smirnov (the original Kain Fuery now Gluttony).
Then there's the Kingdom Hearts seiyuus: Sora (Saji Crossroad), Riku (Setsuna F. Seiei), Axel (Ali al-Saachez), and Alladin (Lockon Stratos)
And also from Tsubasa Chronicle: Saji Crossroad (Syaoran), Michael Trinity (Fai), Captain Barrack Zinnin (Kurogane), Setsuna F. Seiei (Kamui)
Talking to Himself: While the Dylandy twins share the same VA, it's mainly averted in the anime series due to Lyle only getting a major role after the Neil's death, howeverthe live reading in the 2009-2010 New Years Festival has Shinichiro Miki doing a bit of this.
What Could Have Been: According to Wordof God, Gundam 00 was originally supposed to have been fifty continuous episodes like every past Gundam series and not two separate seasons. The story was planned to span 4 years, with the time skip happening in episode 32. The results of the split season were that the time skip happened after episode 25; the first part of the story ended up being put in the first 31 episodes; and that the Lyle/Anew subplot was added into the story.
The Gundams originally had more of a Chess Motif. Their names have changed, but their roles have remained the same.
The Exia was the Pawn Gundam. With short, limited range, it serves its purpose best by charging into the field, annoying and disrupting everything. However, if it ever crosses the chess board, its potential can become limitless.
The Dynames was the Bishop Gundam. Although possessing long range, its limited scope leaves it vulnerable to any unit that can reach it.
The Kyrios was the Knight Gundam. Able to to ignore enemy defenses and attack with impunity, it serves to harass and break up fortifications.
The Virtue was the Rook Gundam. With long offensive range and powerful defensive capabilities, it not only is a dangerous unit on its own, but it also the bodyguard unit for...
The Queen Gundam, or the Nadleeh. With the ability to reach anywhere and anything it wishes, the Queen can dominate the battlefield. However, she takes some time to deploy, and for all her power, she's not invincible and is a prime target to be captured. Also, note the Nadleeh's distinct feminine design, as well as Tieria's own androgyny.
The 0 Gundam was originally meant to be an active command-and-control unit, and thus fulfils the role of the King. By itself, it is extremely weak, but capture or destruction of that unit would lose the entire battle. It also helps that 'Oh' in Japanese means 'King' and well.