Who are two British Prime Ministers with same name?

There have been three British prime ministers with the same name:

1) William Pitt the Elder (1766-1768)

2) William Pitt the Younger (1783-1801, 1804-1806)

3) Robert Cecil, 3rd Marquess of Salisbury (1885-1886, 1886-1892, 1895-1902)

Arthur James Balfour, 1st Earl of Balfour (1902-1905).

The nicknames "the Elder" and "the Younger" are applied retroactively to distinguish between William Pitt Sr and Jr, who were father and son. However, the nicknames were not consistently applied during the time of Pitt the Younger.