mǒu​rén

someone

某人 mǒu​rén
someone pronoun
a certain person or people whose names are not mentioned

Someone sent me an anonymous letter.

myself pronoun
a self-referential term often used after one's surname

A certain Mr. Zhang offers his thanks here.

Frequency

Movie subtitles
34.9 per million appears in 15% of films
Written text
31.7 per million

Sources

Definitions
CC-CEDICT