This is the 3764th most frequent Russian word.
чего
The word "чего" in Russian means "of what" or "of which" and is the genitive case of "что" (what).
In this sentence, "чего" functions as the genitive singular form of "что" and indicates the object of the verb "хочешь" (to want).
Чего ты хочешь?
What do you want?
Here, "чего" represents the genitive singular of "что" in a relative clause to refer to the object of the verb "хотел" (wanted).
Достиг ли он того, чего хотел?
Did he achieve what he wanted?
In this usage, "чего" forms part of the expression "чего угодно," which means "anything," illustrating its role in idiomatic phrases.