People know about you, Commander. Descendant of a watchman who believed that if a corrupted court will not behead an evil king, then the watchman should do it himself–”
“It was only one king,” Vimes protested. “It wasn’t a habit!”
“Sam Vimes once arrested me  for treason,” said Vetinari calmly. “Sam Vimes once arrested a dragon. Sam Vimes stopped a war between nations by arresting two high commands. He’s an arresting fellow, Sam Vimes.

All you ever need to know about Sam Vimes

Terry Pratchett, Thud! 

In this room there was a big wooden chair. In this room there was, by the chair, a rack. The chair was bolted to the floor. It had wide leather straps. The rack held clubs and hammers. In this room, that was all the furnishings. […]

Vimes dragged the largest club out of the rack and stepped swiftly to the wall behind the door. Someone was coming, someone who knew about this room, someone who called themselves a copper…

Getting a firm two-handed grip, Vimes raised the club -
And looked across the stinking room, and saw young Sam watching him, young Sam with his bright shiny badge and a face full of… strangeness.

-Night Watch

‘Quis custodiet ipsos custodies? Your grace.’
‘I know that one,’ said Vimes.  Who watches the watchmen?  Me, Mr Pessimal.’
‘Ah, but who watches you, your grace?’ said the inspector, with a brief smile.
‘I do that too.  All the time,’ said Vimes.