A stubborn person; someone who is obstinate and unlikely to change their opinion or habits easily.
彼は頑固者で、家族の意見にもなかなか耳を貸さない。
He is a stubborn person who seldom listens to his family's opinions.
子どもの頃からの習慣を変えられない頑固者だと言われた。
I was told I'm a stubborn person who can't change childhood habits.
上司が頑固者なので、計画の変更には根回しが必要だ。
The boss is stubborn, so you need groundwork to get changes approved.