If you refer to someone as a nonentity, you mean that they are not special or important in any way.
例句
Amidst the current bunch of nonentities, he is a towering figure...在当前这帮无足轻重的人里面,他算是鹤立鸡群。She was written off then as a political nonentity.她当时被认定是成不了气候的政坛小人物。
英汉词典释义
n.
无足轻重的人
How could such a nonentity become chairman of the company?这样的庸才怎么能当公司的董事长?