This drawing come from a sketchbook at Devon Record Office entitled ‘Portraits of Devonshire Characters’ by Tucker. More sketches in our gallery page.
The title is “Prince of Abyssinia sketched at St Davids station” and is almost certainly a drawing of Prince Alemayehu, son of Tewodros II of Ethiopia, who killed himself after the Battle of Magdala, 1868.
Alemayehu was brought to England by the victorious British, and lived here for about 10 years, until his untimely death at the age of 18 in 1879. During that time he was introduced to Queen Victoria, attended various elite institutions, and apparently passed through Exeter on a train, being here long enough for Tucker to draw him.
The Exeter Memories website has more information about St Davids station.