What is the English word or phrase used to describe who unfairly (tries to) claim, grab or receive rewards/benefits of work or efforts of others?.
One phrase is to take credit for something.
As manager, she felt it was her right to take all the credit for her employee's hard work.
Plagiary is the action of copying another person's ideas or work, without giving them credit.
This gives the verb "To plagiarise" and the agent noun "Plagiarist".
Ironically if I don't cite Michael Rykbin's answer-comment, this answer could make me a plagiarist.