… 之一 (one of)

Great, but not the only one

• … one of (sth)之一zhī yī = "one of (the) …".
• he / him他tāto be / is是shìbest最好zuì hǎo(of / 's)的destudent学生xué shēngone of (sth)之一zhī yī = "he's one of the best students."
• one of (sth)之一zhī yī attaches to the end of a noun phrase.

(Noun Phrase) + one of (sth)之一zhī yī

• one of (sth)之一zhī yī marks the noun as one member of a set.

this这zhèis是shìmost最zuìimportant重要zhòng yào的dereason原因yuán yīnone of之一zhī yī。

• most最zuìimportant重要zhòng yào(of / 's)的decause原因yuán yīnone of (sth)之一zhī yī = "one of the most important reasons."

Implies there are others

• one of (sth)之一zhī yī quietly says the set has more than one member.

Recap

Read the full reference: HSK 4 grammar — Noun phrases.