This is the 18094th most frequent Russian word.
хирург
Surgeon.
In this sentence, "хирург" is used as a subject representing a professional who performs medical surgeries.
Хирург провел сложную операцию.
The surgeon performed a complex operation.
Here, "хирургом" is the instrumental case of "хирург," indicating the role or profession my friend aspires to.
Мой друг хочет стать хирургом, чтобы спасать жизни.
My friend wants to become a surgeon to save lives.
In this sentence, "хирурга" is in the genitive case, used here to specify the role played by the character in the film.