yourself and no one else

Frank is completely selfish - he only cares about number one. 弗兰克极端自私——他只在乎自己。

I'm going to look out for number one (= take care of myself only). 我打算只关照我自己了。

the most important, best, most noticeable, or most famous person or organization in a particular area of activity

She's still the world number one in tennis. 她仍然是世界头号网球选手。

I'm your number one fan. 我是你的超级崇拜者。