I think we are there!
The two
JDs are James Dalrymple and John Dalrymple, respectively Viscount of Stair and 1st Earl of Stair.
They were father and son. There is still an Earl of Stair - they are onto no.14 now.
James was "one of the greatest thinkers on law Europe has ever produced" and his book on Scots law "set the practice of law in Scotland on a sound philosophical basis, almost certainly helped to ensure that Scots law would remain in force as a distinct entity after the union of 1707."
https://en.wikipedia.org/wiki/James_Dalrymple,_1st_Viscount_of_Stair I think that's a lasting positive legacy. I can testify that buying a house under Scots law is (usually) a much more open and honest business than it is under the labyrinthine laws of England!
His son John, on the other hand, organised the Massacre of Glencoe. The right-hand picture is him - see
https://en.wikipedia.org/wiki/John_Dalrymple,_1st_Earl_of_Stair.
In (I think) the short story
The Dagger With Wings, Father Brown contrasts Dundee (who was credited with magical powers) with Dalrymple who did actual evil, using the legal system.
After an enquiry into the massacre, John was dismissed as Secretary of State for Scotland, but regained favour under Queen Anne, who promoted him from Viscount to Earl.
Joint honours to CharlesT and rohan - decide between you who wants to do the next one!
Tim