The 5th Earl of Rosse, William Parsons, was an Irish nobleman born in 1800. He is best known for his contributions to astronomy, particularly through the construction of the Leviathan of Parsonstown, a massive telescope that was the largest in the world during the 19th century. This telescope allowed him to make significant observations of celestial bodies. In addition to his work in astronomy, the 5th Earl of Rosse was also involved in various scientific endeavors and was a member of the Royal Society. He played a key role in promoting scientific research in Ireland and was recognized for his efforts in advancing the field of optics.