Robert Hartman

British author and illustrator. I do not know much about this author, except that he wrote and illustrated a long running younger children's series about the adventures of a slightly eccentric, slightly bumbling old gentleman called Mr. Buffin. One of these adventures included his horse, a self-opinionated grey mare. I do not think horses featured in any of the others however. All the books in the series are fairly rare, including the horse title.

Horse & Pony Books:

MR. BUFFIN AND HIS GREY MARE
(ROBERT BARKER 1937)
ILLUSTRATED BY THE AUTHOR
Reprinted in hardback by original publisher.
Reprinted in hardback and also possibly paperback by Morrison & Gibb in the 1950s.
Fairly rare
SUMMARY: Part of a longer non-pony series about the bumbling yet charming Mr. Buffin. Variously described as number 3 or number 7 in the series which ran to at least 23. In this adventure, Mr. Buffin's grey mare lets her rider know what she thinks of his decision to take her for a ride on a Sunday when he should have been at church! The story is aimed at younger readers.

Collectors Info:
Can be quite hard to find, although there are usually one or two copies around in the UK.. Prices can vary quite a lot. Very hard to find outside of the UK however.