In Ancient Greek, the nominative case is used for the subject, subject complement, or words used in apposition to the subject of a sentence.

EX:
  • John killed the cat. (subject)
  • Mimes are evil. (subjective complement)
  • Jane, my alternate personality, is a raving lunatic. (appositive)

Another node on Ancient Greek grammar, by everone's favorite Hellenic pedant. forward.