me-za-me-ro:

Thank you!

Well, russian names have different forms.

1. A formal form is official and is used in documents, in formal communication, when we address a person with a higher social rank, a senior person, or simply a person who we respect. Usually we use formal names with patronymics (but I don’t know the name of Viktor’s father). So Viktor - is a formal name.

2. A colloquial form is used when we address a person in informal communication, acquaintances, friends, family. So Vitya is a colloquial form. (I honestly want Yuuri to call him Vitya so much unngh).

There is also a stylistically lowered form - Vit’ka - but it has a bit disrespectful attitude if used not by close friends or relatives.

3. A diminutive form is used in friendly and intimate communication, when we address a person we are close with. These forms are usually emotionaly colored, and express our warm, tender attitude to a person. So Vitechka, Viten’ka, Vityusha are diminutive forms.