Willie-Jay is one of Perry's few friends in In Cold Blood and he is the only one of those friends who attempts to change Perry's attitude and to save him from future violence. Willie-Jay is honest and respectful with Perry, a combination of traits unique in Perry's experience.
An older man, Willie-Jay sees Perry as a person who needs help and he astutely recognizes that one thing Perry lacks especially is self-esteem. By acknowledging Perry's intellect and his talent, Willie-Jay ingratiates himself with Perry and becomes a mentor figure. He always takes Perry's side and tries to build him up while also telling the truth.
This situation does not last, however, because Willie-Jay insists on joining religion to Perry's path to reform. Perry's experience with the nuns in the orphanage where they beat him and berated him completely soured him on religion. When Willie-Jay insists on talking about religion, Perry looks for friendship elsewhere.
Importantly, Perry never stops feeling that Willie-Jay had his best interests in mind. Perry continues to feel fondness toward Willie-Jay and seeks him out in Kansas.
Willie-Jay is a friend of Perry's who is being released from Kansas State Penitentiary. Willie-Jay is described as "a slender Irishman with prematurely gray hair and gray, melancholy eyes." He is the chaplain's clerk who is in jail for a series of small robberies, and, after Perry approaches him, he seeks to become friends with Perry to have a better chance to bring Perry to salvation. Willie-Jay senses that Perry is “a poet, something rare and savable.” Perry paints a technically adequate portrait of Jesus, but he never truly reforms himself or finds Jesus, which Willie-Jay knows. When Perry is about to be released from jail, Willie-Jay writes him a heartfelt letter warning him about his tendency towards explosive reactions. However, Perry feels connected to Willie-Jay, because he is one of the few people, Perry thinks, who understands his worth. When Dick proposes that Perry return to Kansas, part of why Perry accepts the invitation is to see Willie-Jay again after Willie-Jay is released from jail.