When researching the cult and literature of saints, one is very often dealing with figures whose historicity is doubtful, and sometimes even figures that clearly have not existed. In some cases, the non-existent figures were not the saints themselves, but instead people featuring in the stories about them. These secondary figures of historical non-existence very often contribute to obscuring that kernel of the saint's legend which does seem to have some historical basis. This is the case with Saint Richard and King Otto of England.
In my research I recently came across the story of Saint Richard in an incunabula housed at the university library of the University of Southern Denmark (Syddansk Universitetsbibliotek). According to the front matter of the book, replicated by hand after the original printed front matter was somehow lost, the book is a collection of saints' lives in German called Dat Leuend der Hÿlghen, or The Lives of the Saints, printed in Lübeck in 1492.
Saint Richard, son of King Otto of England
Dat leuend der hÿlghen, a collection of stories about saints, Lübeck, 1492
Incunabula RARA M 15, Syddansk Universitetsbibliotek
I was quite intrigued to see this story of Saint Richard. I had never heard of him, and since I have been working quite a bit with English saints I was excited to learn of one more. As the vignette to the story indicates, Richard was noted as a pilgrim, shown by the pilgrim's hat and the pilgrim's badges of the scallop, which is the symbol of Santiago in Compostela, but which is also seems to be used as a shorthand for denoting the pilgrim in medieval iconography. I was, however, very surprised to read that he was the son of King Otto of England, because there has never been any such king in the history of the kings of England.
As for the historical nature of Saint Richard, this is, according to David Farmer, a name that is given to the father of Saint Willibald, Saint Winnibald, and Saint Walburga, three figures whose historicity is certain, and who were Anglo-Saxons pilgrims who became important ecclesiastical figures in Germany. The story of their pilgrimage were written down by the nun Huneberc of Heidenheim (fl.780) in the book Hodoeporican, and Reginald of Eichstatt (d.991) appears to be the one responsible for introducing Richard as their father. According to the legend, Richard died at Lucca where his relics were venerated "at least from the twelfth century" (Farmer 2004: 454).
Accordingly, Saint Richard is a figure of dubious historicity, woven around the possible fate of the historical father of the three Anglo-Saxons who became saints in their turn. It seems clear, however, that Richard was not at any point a king. What then, of the mystical King Otto of England?
It is possible that Otto is here the result of an intended German translation of Offa. This is a name of two historical kings, the eldest being a king of the East Saxons who was active around 709, the youngest being the more famous king Offa of Mercia (d.796). Chronologically speaking, if Otto is indeed Offa, it is likely to be Offa of the East Saxons. But even if this is the intended identity of Richard's father, it is safe to say that Richard himself does not appear to have ever been the son of Offa, and that this is rather a product of later legends accrued around the cult of Saint Richard who was venerated not only in Lucca but also in Eichstatt where Reginald wrote his legend.
Farmer, David, Oxford Dictionary of Saints, Oxford University Press, 2004
Huneberc's Hodoeporican: https://sourcebooks.fordham.edu/basis/willibald.asp
Dat leuend der hÿlghen, a collection of stories about saints, Lübeck, 1492 (Incunabula RARA M 15, Syddansk Universitetsbibliotek)