Who is Philip Philippovich Preobrezhensky from Heart of a Dog and what is their importance?

Philip Philippovich Prebrezhensky is a highly acclaimed doctor living in Moscow. He is much in demand, and his office is always full of patients, many of whom have socially unacceptable problems and trust him implicitly. Also living in his seven-room apartment are the Zina the maid and Darya the cook. Philip plans to transplant the pituitary gland and testicles of a human into a dog in order to determine whether such a transplant would be viable between humans.