Well done for getting the name correct it is Captain Morgan, Captain Edward Morgan to be precise. He was reportedly killed in the English Civil War near to Llys Helyg and the stone marks his grave.
There is a building nearby called Plas Captain and I'm not certain if he had any connection with that building.
I've copied something about him in case anyone is interested.
“On the east-side of Mostyn pool, in Tegin mountain, is a grave bounded on
> each end by a rude stone, above four feet high. It contains the remains of
> captain Edward Morgan, of the adjacent house of Plas Captain, and of the
> respectable family of the Morgans, of Gwlgray, in the adjoining parish of
> Llan Asaph. Some years ago a person of strange curiosity open the grave,
> and found a skeleton. On the head was a red cap, I think of velvet, and
> round his neck a silk handkerchief. By him lay his sword, and his helmet;
> and beneath the skeleton two bullets, which had fallen out of the body on
> its dissolution; all which verify the report of his having been slain in
> battle, or in some skirmish during the civil wars, and that he was
> interred, according to his wish, under the spot on which he fell