
One of the things that always springs to mind about Westminster Hall is the amazing hammerbeam roof, for which we have our 14th-century monarch, Richard II, to thank. He didn’t build the hall itself, of course, because that accolade goes as far back as King William II “Rufus” in 1079. And Rufus was disappointed in his great building, having envisaged something twice the size!
At the Hall only two lyings-in-state having been of commoners, William Gladstone and Sir Winston Churchill. Everyone else to have had this honour was of royal blood, either monarchs or their consorts.
Strangely, it’s a very short list, not because no other monarch lay in state, but because all those who did were elsewhere, e.g. St Stephen’s Chapel, Westminster.
On a number of occasions in the days after the passing of HM Queen Elizabeth II, I heard TV presenters state that Gladstone (1898) was the first person to lie in state in Westminster Hall. Then it was added that the only others were monarchs. Eventually it was clarified to recent lyings-in-state.
According to this site which should indeed know what it’s talking about, the following persons have lain in state in Westminster Hall:-

Tebby, Arthur Kemp, 1866-1957
Date: 1898


All the persons mentioned above were in their coffins on the catafalque, but back in medieval times their bodies were displayed, duly enrobed and crowned. And yes, there was at least one great royal figure from back then who lay in state in the hall in the 14th century.

I speak of Edward of Woodstock, Prince of Wales, the “Black Prince”, , who was the father of Richard II and died on 8 June 1376. The prince was taken to lie in state in Westminster Hall until September 1376. Whether his body was displayed or not I don’t know, but I suspect it was. He was then taken on his long funeral procession to Canterbury, where he was finally laid to rest on 29 September 1376.
This tomb there can still be seen, together with replicas of his achievements (the original still exist but are being preserved).
If there were other medieval figures who lay in state in Westminster Hall, I am not aware of them.