The most common Korean word for “that person” is 그분 (geubun). There is one more word with a similar meaning — compare them below. 「that person」는 한국어로 그분.
that person (honorific)
TOPIK 2 · pronoun
that gentleman; that lady (honorific)
TOPIK 2 · pronoun
Words and levels: TOPIK I essentials (National Institute of Korean Language standard curriculum, KOGL Type 1) · examples: Cheesepotato
치즈감자