A Human Reform League mobile suit commander known as the "Wild Bear of Russia," but he's actually a very chill guy and is one of the only people who is shown to be capable of outwitting Sumeragi. He is such a good pilot, that even at the age of 43 he can keep up with teenagers, even though it's an anime. He a father figure to Soma Pieries, instilling in her a sense of kindness that took even him by surprise. (He apparently failed in raising his own son Andrei though, according to said son, but then, Andrei is just a Jerkass.) Sergei refuses to join A-Laws, and will smack the fools who pass information about him to them.