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His name was William de la Hay. If you look very carefully you might be able to find his name on the tomb

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Thomas, fourth of Locherworth, to the heiress of Sir William de Coningsburgh, which brought to the family the lands of Tullybothwell in Clackmannan.
From this couple descend the great northern branch of Hay of Lochloy. The effigy of Sir William Hay of Lochloy (d. 1421) can still be seen in full armour in Elgin Cathedral

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William de la Hay.— Elgin Cathkdral.
Tliu now almost quite illegible inscription on this tomb (fig. 49) reads, " Hie jacet Wills de la Hay quondam dominus de Lochloy qui obiit viii die niensis decerabris anno Domini mccccx.ki." His family are stated to have held the house, park, and barony of Inshoch for upwards of four hundred years.
The effigy has upon the breast three shields— the paternal bearings of the family of Hay ; and although at present appearing as a detached monument, appears as if it had at one time been recessed.

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Sir William (Knight) "Laird of Lochorwart and Yester" "High Sheriff of Peebles (1387)" de la Haye (Hay) of Lochorwart and Lochloy (born 1375)

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Hay of Lochloy Argent, three escutcheons Gules within a bordure Gules