Who is Kiril Kirillovich Rublev from The Case of Comrade Tulayev and what is their importance?

Rublev is an old man who works at the Academy of Sciences. He is a scholarly man who is smart and passionate about music. He is tall, thin, and broad shouldered, but he has begun to stoop in the last two years, not because of age but because of anxiety. He has a scanty beard and a big, bony nose and bushy eyebrows. The kids in the neighborhood call him Ivan the Terrible, and he does resemble portraits of the Bloody Czar. He is eventually arrested and charged with being part of a plot to kill Comrade Tulayev. He is executed for the crime.