Chiho G. answered 11/11/19
Chiho: Bilingual Japanese/English Professional Tutor
I think you have learned the position word like 辞書はつくえの上にあります。A dictionary is on the desk. 辞書はつくえの上にある。にあるindicates where an object is placed. In this case, "the person" is placed in the important position, a leader of the country. However, you can't use "the person, 者" with the word, "にある", so we need to look for something else other than "者" or "人"to adjust ある, and that is 立場, position. If you really want to use both "person" and "ある", it will be "である". E.g. わがはいは猫である。I'm a cat. by Soseki Natsume