This is the 19317th most frequent Korean word.
알렉세이
"알렉세이" is the Korean transliteration of the Russian name "Alexei."
In this sentence, "알렉세이" is used as a proper noun to refer to the name of a person.
알렉세이는 러시아에서 온 친구입니다.
Alexei is a friend from Russia.
Here, "알렉세이" is the subject of the sentence, indicating the person being talked about.
알렉세이가 테니스를 잘 친다고 들었어요.
I heard Alexei is good at playing tennis.
In this instance, "알렉세이" is the object of the verb, indicating the person whom the action is directed towards.