Who is Donatas Banionis from Sculpting in Time: Reflections on the Cinema and what is their importance?

Banionis was the star of Tarkovsky's Solaris film. Unlike actor Solonitsyn, Tarkovsky had a difficult working relationship with Banionis, who was endlessly analytical and who prodded Tarkovsky for extensive background information on the character he played. Banionis was a theater actor before he was a film actor.