Henry Campbell Bannerman
I have never met a great public figure who so completely won the attachment and affection of the men who came into contact with him. He was not merely admired and respected; he was absolutely loved by us all. The masses of the people of the country, especially the more unfortunate of them, have lost the best friend they have ever had in the high place of the land. ... He was a truly great man. A great head and a great heart. He was absolutely the bravest man I ever met in politics.
Sir Henry Campbell-Bannerman, GCB was a Liberal statesman who served as prime minister for about three years before resigning over his health. He was also the first person to be known officially as prime minister whilst holding the office, although the term is now retroactively used to apply all the way back to Sir Robert Walpole. In the time of William Pitt the Elder, the term "prime minister" was an insult used to mean "the king's favourite creep".
Campbell-Bannerman's premiership saw the Entente with Russia in 1907. In that same year, he became the Father of the House, the only serving British prime minister to do so (Winston Churchill and James Callaghan would do it after they left office). But poor health took its toll. Campbell-Bannerman resigned but died before a successor was named, and is the only prime minister to die at Number 10 (even if he was technically the former prime minister at the time).