Government Official, Public Servant
A person with duty is someone who works for the government... a government official or public official.
This is a jukugo word, which usually means on'yomi readings from the kanji. Since 人 has two on'yomi readings, here's a mnemonic to help you remember which one to use:
A public official recently declared that all the yaks at Nintendo (やくにん) are going to be kicked out. You didn't know that Nintendo has resident yaks? Well it does, but not for much longer. But who will take care of all the Nintendo yaks now?! Maybe you could take one in!
A public official came today.
If you graduate from college and pass all tests, you can become a government official.
Even the official is a human with a heart.