THE ONE WHO = AZ,  AKI…, …

As you see, the Hungarian equivalent is:

Az, aki…,… OR
Aki…, az…

Examples:

Aki délben napozik, az hamar leég.
Az, aki délben napozik, hamar leég.
The one who sunbathes at noon, will get a sunburn soon.

’Az’ and ’aki’ can vary depending on the sentence:

Aki embert öl, annak börtönbe kell mennie.
Annak, aki embert öl, börtönbe kell mennie.
The one who kills people has to go to jail.

Of course you can write different sentences similar to English:

The one who learns Hungarian is likely to be pretty ambitious.
Az, aki magyarul tanul, eléggé törekvő lehet.

He who learns Hungarian is likely to be pretty ambitious.
Az, aki magyarul tanul, eléggé törekvő lehet.

The person who learns Hungarian is likely to be pretty ambitious.
Az az ember, aki magyarul tanul, eléggé törekvő lehet.

The people who learn Hungarian are likely to be pretty ambitious.
Azok az emberek, akik magyarul tanulnak, eléggé törekvőek lehetnek.

Those who learn Hungarian are likely to be pretty ambitious.
Azok, akik magyarul tanulnak, eléggé törekvőek lehetnek.