Decimus Greenshaw is a non-canonical character created for the 2013 ITV adaptation of Greenshaw's Folly. He was the father of Katherine Greenshaw and her two sisters and an eminent scientist. His house, Greenshaw's Folly, had a laboratory in which he conducted medical experiments. Decimus Greenshaw was long since deceased during the time of the events in the episode and he is not seen onscreen, only frequently mentioned. His long unused laboratory was kept locked up. Access to it was forbidden and it was a source of mystery to the various visitors to the house.
During the course of the episode, it was revealed that Decimus had been conducting experiments with a view to developing a cure or vaccine for polio. This was an urgent effort which he termed "the Great Race". From 1900 to 1910 (some 40 to 50 years before the time of the events in the episode) he had used orphans from St Faith's Orphanage as guinea pigs for his experiments. Many of the children contracted polio and died as a result.
In addition to this, Decimus was also a hard man to his own family. His children were afraid of him and he cut his daughter Nettie Greenshaw off from the family when she married someone he considered unsuitable.
In the original story, Katherine Greenshaw's father is not named nor is there any background given about him. The only feature in common with Decimus is that he also cut Nettie off after her marriage.