Remind me, which is the correct one: "Nosferatu Zodd", or "Zodd the Immortal"?
Trick question, of course: it's both.
As you can see in the image above, ノスフェラトゥ (Nosferatu, spelled like the title of the 1922 movie) is written next to 不死の. Text written like this is called furigana, and is used to indicate how to pronounce a word.
Typically, hiragana will be written above some kanji to make reading them easier. In this case, katakana is used because "Nosferatu" is a foreign word. This is something Miura did regularly in Berserk in order to convey the meaning of a word while giving it a "fantasy" name. For example 妖精 (YOUSEI) with エルフ (ELF).
Anyway, the word 不死 (FUSHI) means "immortality". Its construction is simple: 死 (SHI) means death. 不 (FU) is a prefix that negates whatever comes after. の (NO) links this to the name ゾッド (ZODDO). The result is "Zodd the Immortal" when you read the kanji. However the furigana takes precedence, and so it should be read as "Nosferatu Zodd".