The black servant of Sir William Penn.
Since we can never know about the real Jack, I find it touching that Clive Mantle has published a children's book in 2020 about his adventures with Mingo during the plague and the Great Fire. They were the heroes of the day, as their friend, Freddie (who worked for Pepys in the story) was chasing the Diary and the cheese.
In this write-up of ‘In the City of Fortune and Flames’ the author hopes schools will use the book as there few dealing with slavery, age appropriately. And pandemics, come to it.
I've not read the book, so I trust it will say that the life of all servants was pretty miserable at this time, and misbehavior was punishable by exile in Barbados for people of all skin hues, from pink to mahogany. We know that Mingo was specifically provided for in Admiral Batten's will, which indicates his high regard for the man. Hopefully Admiral Penn felt the same way about Jack. There were many valued free black and brown sailors in the Navy at this time ... and free traders with their families in London, Bristol and Edinburgh. I hope Mantle hasn't turned Restoration London into Georgian London.
The review by the author is at
You can skip the first few paragraphs which deal with Mantle's previous book about Egypt.
Chart showing the number of references in each month of the diary’s entries.