Horace Walpole on Richard III

According to the official website of the Richard III Society, in their primer "A Brief Biography and Introduction to Richard's Reputation" by Wendy E.A. Moorhen:

The Great Debate, as the study of Richard's reputation became known, truly began in the seventeenth century when Horace Walpole wrote his Historic Doubts and rattled the cages of the traditionalists. That debate is not yet over, with the majority of the British historical academic community still promoting Richard as an infanticide. Some academics have acknowledged that Richard was a talented administrator and that he cannot be held responsible for the deaths of Henry VI and his son, but their overall assessment is still that of an evil and avaricious man.

This passages suggests that, far from being ignored, Walpole's text stirred up the following centuries of argument as to the truth about Richard III.

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Although I have not been able to find a scholarly article that particularly focuses on Walpole's Historic Doubts on the Life and Reign of King Richard III (1768), I have been able to locate several articles that reference the text and may give light to your research.

In "Thomas More and Richard III" (Renaissance Quarterly, Vol. 35, No. 3 (Autumn, 1982), pp. 401-447), Elizabeth Story Donno suggests that More's representation of Richard as a wicked king offered such a rich and interesting history that it proved hard to refute. (More's status as a saintly martyr and a learned man also probably played into the strength of his assertions, making it difficult for a scholar like Walpole to contradict.)

As Story Donno notes:

The "historical" influence of More's "story" of Richard III was longlasting, extending not only throughouthe century of the Tudors but continuing into later centuries, with Horace Walpole's Historic Doubts (1768) the first effective challenge to its received position in English historiography.

(Also of note, Shakespeare's entertaining and enduringly popular play Richard III, though obviously historically inaccurate in many ways, drew on More's version of history and no doubt contributed to the lingering bias against Richard, at least among the general public and possibly even among scholars.)

In "Jacobean Historiography and the Election of Richard III"(Huntington Library Quarterly, Vol. 70, No. 3 (September 2007), pp. 311-342, David Weil Baker alludes to Walpole at the end of his article which focuses on how several historians before Walpole began to question the idea of Richard III as a tyrant. This is Weil Baker's abstract:

In the early seventeenth century, William Camden, John Speed, and Sir George Buck began, in varying degrees, to question Thomas More's influential depiction of Richard III as a nefarious tyrant whose reign lacked all legitimacy. David Weil Baker argues that chief among the factors provoking this revisionism were the discovery by Camden of the long buried parliamentary Act of Settlement (1484) and the Jacobean political controversies that made this discovery seem to be of contemporary as well as historical interest. For in addition to bolstering Richard's right to rule, the Act of Settlement made claims about the authority of Parliament in matters concerning the succession to the throne—an authority that was conspicuously not acknowledged by James I. Though Camden, Buck, and Speed did not bring about a widespread re-evaluation of Richard, a lasting effect of their efforts was to write Parliament into his story and to make that story relevant to the issue of what role Parliament should have in the succession.

Although I realize that this does not constitute a true criticism of Walpole's text, you may find it useful to place Walpole in context. Although his Doubts may remain one of the earliest and most influential attempts to reevaluate Richard III, it was not necessarily the first.

The last two articles mentioned are available through JSTOR.