Complex sentence: His boss is a strict unmarried woman, Lyudmila Prokofyevna Kalugina, nicknamed "our" by her subordinates, who has confidence problems of her own hidden behind her gloomy humorless demeanor and plain old-fashioned look.
Split into simpler sentences: His boss is a strict unmarried woman, Ludmila Prokofievna Kalugina, nicknamed "our" by her subordinates. She has some self-confidence problems, hidden behind her gloomy humorless demeanor and plain old-fashioned look.