Complex sentence: Dr. Khan, who was a key figure behind Pakistan's clandestine nuclear weapons project and began working for the government of Pakistan in 1975, has described Gen Ali Nawab as a "competent engineer and thorough gentleman" in one of his articles.
Split into simpler sentences: Dr. Khan, who was a key figure behind Pakistan's clandestine nuclear weapons project and began working for the government of Pakistan in 1975. Khan has described Gen Ali Nawab as a "competent engineer and thorough gentleman" in one of his articles.