always wanting more of something
insatiable - greedy
The term ‘insatiable’ is typically used in relation to a desire or need that is, figuratively, too great to be satisfied. If, for example, you were to say that somebody has an insatiable appetite, you do not mean that they could eat continuously and never get full, you are instead indicating that they eat more than what would be considered normal.
Gary is the hardest working person I know. He just has an insatiable desire to succeed.
My son is nearly 5 now. He is insatiably curious about the world around him.
One of the things that marks Sandra out as an historian is her insatiable thirst for knowledge.