Jimmy has a personal vendetta against Howard Hamlin.
Jimmy blames Howard for the death of his brother, Chuck, a former colleague and firm partner of Howard’s at Hamlin Hamlin & McGill (HMM). Chuck took a leave from the firm when he started suffering from an illness, claiming a sensitivity to electromagnets, that prevented him from leaving the house.
After Howard forced Chuck to retire from the firm, Chuck died by suicide in a housefire he started.
For years, Jimmy wanted nothing more than a seat at the table and to work at HMM as well. Not seeing his brother as good enough, Chuck prevented that. At the time, Howard respected those wishes.
On season five, feeling responsible for Chuck’s death, Howard offered Jimmy an opportunity to work at HMM once he saw the business he started to build as Saul Goodman, but Jimmy was offended. Not only did it look like a pity hire, but it also came a little bit too late.
Instead, Jimmy decided to dedicate himself to making Howard’s life miserable and besmirch his name. On season five, he threw bowling balls at his car and sent prostitutes to disturb a lunch meeting.