Homer Pinkerton was a professor who helped create the Memory device that allowed Spectrum to remove specific memories and replace them with harmless ones.
He lived down the street from Ruby and took care of her when she was young. He hid the secret to SME (Specific Memory Extraction) in her eyes meaning that whoever needed the secret would have to find Ruby first. He did this because he said that Ruby was the smartest child he ever met. He told Ruby this in a note, concealed inside the blue dog bone that he left with Mrs Beesman.
He was dead before the start of Ruby Redfort, Blink And You Die, and was possibly murdered by the Count or Casey Morgan.