In 'The Graveyard Book' by Neil Gaiman, why is one 'Jack' named for a historical person

Question

The book features a group of characters who are members of a fraternal organization, and call themselves:

the Jacks of All Trades, or the Knaves, or by other names. We go back an extremely long way. We know ... we remember things that most people have for- gotten. The Old Knowledge.

There are five of them and they are all called Jack:

• Jack Nimble
• Jack Dandy
• Jack Frost
• Jack Tar, and
• Jack Ketch

It is easily seen from their physical and behavioural descriptions that these characters are, or are drawn with reference to; Jack-be-Nimble, Jack-a-Dandy, Jack Frost, Jack Tar and Jack Ketch.

Four of the five are therefore named for Nursery Rhymes or Personifications, but Jack Ketch is named after a real, human person. The Jacks of All Trades are clearly not exactly human, or not 'still' human. Are we to understand that, like the ghouls elsewhere in the book, they have been human and have assumed new names after their transition to another state, or that they are the originals whose names have found their way into Human culture. In either case, why four 'unreal' Jack names and one 'real' one?. Why is one of these not like the others?

Answer 1

"Jack Ketch" became a nickname for executioners in general. The hangman, any hangman, was called Jack Ketch centuries after the death of the original.

See for example A Classical Dictionary Of The Vulgar Tongue, 1711.

Oliver Twist uses the name generically for the hangman.

So, really, it's the same as the others, a generic term for a hangman. The fact that it came from a specific individual does not change that it's a generic term.