Mihalyi of Mercere
Mihalyi of Mercere was the listed as the current primus of the house in the Houses of Hermes sourcebook. He is very likely non-canonical, and is quite a bit unusual amongst characters in publication history, in so far as he is not mentioned in previous or subsequent sourcebooks. Insatella of Mercere was the listed prima in the Second Edition Order of Hermes sourcebook, the Third Edition Tribunals of Hermes: Rome sourcebook and in the Mercere section of the Fifth Edition Houses of Hermes: True Lineages. Given the unusual place in the publishing history Houses of Hermes holds combined with the treatments of the primus in all other editions, it's likely that Mihalyi simply does not exist even within history in Fifth Edition.
According to Houses of Hermes, Mihalyi was a redcap primus who was adverse towards nobility in general because of prior treatment by an unnamed baron.