Constantin Stanislavski was a Russian actor and director who developed an influential system for actor training and character development. His system strives to make performances feel "real" rather than artificial by drawing on actors' own experiences and imagination to develop their characters from the inside. It involves techniques like analyzing a character's objectives, determining their inner motivations, using imagination and concentration to fully inhabit the character, and connecting physically and emotionally. Stanislavski's system had a major impact on modern acting and is still widely used today.