In (modern) Greek, there are four cases for nouns and names, depending on their position in the sentence; nominative, accusative, genitive and vocative. Nominative is the subject in a phrase, accusative is the object of the verb, genitive is the possessive case, and vocative is used, for example, to call somebody. "Dimitrios" is a formal name, that no one really uses. Instead, the nominative case of my name is "Dimitris" and all other cases are "Dimitri". (Don't generalize this to other greek names, however)