Pre-eminent is the adjective. A pre-eminent person, group, or thing is much more important, more powerful, or plainly better than the others of its kind — not just good, but the one that stands at the top. It is a formal word. You will meet it in writing about scholars, artists, companies, and nations (“the pre-eminent expert,” “the pre-eminent power in the region”). In speech, people often just say the leading or the top. British English likes the hyphen (pre-eminent); American English often writes preeminent. It does not simply mean “famous.” You can be famous and still not be pre-eminent, and a quiet specialist can be pre-eminent in a small field that most people never hear about.