nieustępliwy zawzięty in inglese:

Oliwia is a tenacious person.

2 a: persistent in maintaining, adhering to, or seeking something valued or desired <a tenacious advocate of civil rights> <tenacious negotiators> b: retentive <a tenacious memory>

"You have to be really tenacious," she said of her learning experience.

There has been tenacious local opposition to the new airport. The baby took my finger in its tenacious little fist.

He's a tenacious guy who always manages to come out on top. He's the kind of guy who can turn any situation to his advantage.

To survive in a hostile environment, one must be able to improvize and be tenacious.