EDIT: disregard information below about the Queen of Sheba. This is a 17th-century AD painting originally from a church in Lalibela, Ethiopia and now housed in the Addis Ababa National Museum. It depicts Saint Mercurius as an equestrian figure. Source. See also Job K. Savage (2010), p. 74 for an illustration and description of the painting executed in the Second Gondarene style of Early-Modern Ethiopian art.

Originally a wall painting in a church in Lalibela, Ethiopia, the piece is now in the collection of the National Museum in Addis Ababa, Ethiopia.

Initially, seeing the lance, I thought the painting depicted St. George, the patron saint of Ethiopia. In Ethiopian art, as in other traditions, St. George is depicted on a horse skewering a dragon with his lance. More recently, though, I have seen the figure described as the Queen of Sheba, another figure central to Ethiopian history.

In looking at someone else's photograph that shows more of the painting, I didn't see a dragon, which is an important, nay, indispensable, element in the iconography of St. George: no dragon, not St. George.

On the other hand, the horse, with its ruff, elaborately decorated bridle and pretty collar of bells, looks more regal than the rider. If this is the Queen of Sheba, she's either traveling in disguise, or her tastes are simpler than one would expect of someone of her rank, accomplishments and connections.

Another explanation may lie in the conventions of Ethiopian painting at the time this piece was executed. Perhaps Queens and other notables were depicted in plain attire for a reason. If that's the case, I'm off the hook, since I don't know enough about Ethiopian art of this era to discuss it in anything but the most superficial and derivative terms.

The Queen of Sheba is certainly more imposing than this in the famous painting by The Most Honourable World Laureate Maître Artiste Afewerk Tekle that hangs In St. George's Cathedral, Addis Ababa, Ethiopia. My photo of that painting appears below.