hard worker; hardworking person
Describes a person who consistently puts in effort; often used admiringly.
She's a hard worker, so I'm sure she'll succeed.
A hard worker, he studies until late every day.
努力家 is a noun describing a person known for making great effort, while 勤勉 is an adjective describing the quality of being industrious itself.
Compound of 努力 (effort) + 家 (suffix for a person with a certain characteristic).