An emperor is the male leader of an empire. Empress is the feminine form and can refer to a woman who holds the rank of emperor (empress regnant), a wife of an emperor (empress consort), or a widow of an emperor (empress dowager). Emperor is the highest temporal title there is, outranking even king. The only emperor in the world today is Emperor Akihito of Japan. However, at the beginning of the 20th century, other countries had emperors, including Austria-Hungary, China, Germany, the Ottoman Empire, and Russia.
Emperor is also a species of penguin.