Although, those who didn't agree with the above theory usually assumed the man to be Eumenes anyway, for various reasonsnote The historical Eumenes was from Thrace (modern-day Turkey) and is suspected to have Scythian ancestry; Scythians were known for their long black hair, whereas the Greeks would usually cut it short. Eumenes also began as Alexander's secretary rather than as a warrior or soldier, which would explain the character's outfit of a robe rather than armor. Coincidentally, Eumenes was known for his loyalty to Alexander and his lineage, a trait many associate with Waver.. Later series like the Sensha Otoko parody manga, Lord El-Melloi II Case Files and Fate/Grand Order would later imply it heavily before he was officially confirmed as such.
The Other Darrin: Completely averted in the Japanese version. All the cast members from the drama CDs reprise their roles for the anime series.
For the English dub, this trope is played straight for almost every character that appears both here and in the anime of Fate/stay night, due to the dubs being handled by entirely different companies. This is especially notable in the cases of Artoria, Gilgamesh, Kiritsugu, and Kotomine, since the actors who played them in Fate/stay night are also in the dub of Fate/zero, but they play different characters. The sole exceptions are Mela Lee and Stephanie Sheh, reprising the roles of Rin and Ilyasviel respectively.
There would've been a subplot where one of Assassin's personalities, a little girl, got separated from the others and forgot her identity. After mistaking her for one of Caster and Ryuunosuke's kidnapped victims, Waver takes her in. Rider knows what she really is, but keeps quiet out of respect for Waver's chivalry. Waver and the girl bond, but when Kotomine uses a Command Spell to make all the Assassins attack Rider's party, she regains her memory and joins the attack. Waver is devastated by her death, but toughens up and moves on, as the subplot was meant to be a step in his growing up.
Nasu said if he wrote the series, he would have made Rider very similar to Red Saber.
Before Gilles de Rais was chosen as Caster, Gen Orobuchi wanted to use a Chinese Xian. The reason he didn't was because Nasu ruled that Eastern heroes can't be summoned in Fuyuki's system (fake Assassin in stay night was explicitly a case of the rules being broken by Caster).
Toshiyuki Shirai, an animation director, said the original plan for Lancer's death scene was that he would turn into particles of light and fade away. Then he decided it would make his Dying Curse more dramatic if his body crumbled away while releasing a black mist.
Originally, Kariya's brother Byakuya would either not appear or be a brief background character. The scene where Kiritsugu raids the Matou mansion was going to have him simply conclude no one was home and move on. Then Urobuchi thought "there isn't enough violence today", so they had Kiritsugu run into Byakuya and interrogate him.
While it's not exactly a surprise to anyone familiar with Alexander the Great and his widely speculated bisexuality, Gen Urobuchi confirmed the orientation for his Fate/zero counterpart when discussing how events would have turned out if Kayneth summoned Rider as he intended instead of Lancer (Answer: Rider would have attempted to bed Sola-Ui and Kayneth).
The historical Gilles de Rais is widely speculated to have been gay or bisexual; likewise Caster is described as being attracted to both tomboyish women and feminine men.