He was the first prime minster to have not previously held a ministerial office. There has only been three after him; that this applies to: Ramsay Macdonald, Tony Blair and David Cameron.
When King George III had forced out the Duke of Devonshire, he installed Rockingham.
Rockingham abolished the unpopular cider tax but instead, started window tax.
George III soon became fed up with Rockingham and replaced him with Pitt. However Rockinham did return as prime minster in 1782.