Ronald Callendar is a prominent scientist, and with regard to his professional career...
…[h]e displays a cool demeanor and single-minded interest in his work.
However, as a father, Callendar is found wanting: there has been little connection between father and son, and no affection. Mark's friends are surprised that Mark's father seems concern that the police discover the truth behind Mark's suicide, as Callenar is such a distant father. When Sir Ronald is first interviewed after the death of his son, he is "oddly detached" regarding his dead son. We learn that he has denied his son as a person and a family member. Callendar's poor example of a father is further exposed when the reader compares him to Dalgliesh and Pryde, who act as "spiritual fathers" to Cordelia.
Callendar was an unfaithful husband when we learn that the woman who Mark believed was his mother simply raised another woman's son by Ronald Callendar. Sir Ronald is a scientist whose existence, and the world he lives in, has no room for love. He is an oppressive personality with little concern for others: he brings Lunn home from an orphanage, but will not allow Lunn to be trained as a scientist—as his intelligence deserves—but only as a simple lab assistant.
When it is revealed that Sir Ronald murdered his son as Mark was ready to sever the connection between the two, Callendar kills Mark and tries to conceal it as some kind of "sexual event," as Mark's body was originally found by Isabelle de Lingerie in women's clothes.
Sir Callendar has little character as seen in how he has treated Mark, Lunn and Elizabeth Leaming, Marks biological mother.