[noun (scope/group)] + きっての + [noun (person/thing)]
Note: きっての is a fixed expression; it always modifies a following noun.
きっての is an emphatic expression meaning "the most … of all" or "the greatest … in". It is used to single out something or someone as the most outstanding within a particular group, organization, or area. Despite its appearance, this is a fixed expression derived from the classical verb きる切る in its て-form, combined with the attributive particle の. It always modifies a noun.
きっての is almost always preceded by a noun indicating the scope or group (marked by で) from which the superlative is drawn, and followed by the noun being described.
きっての carries a strong, somewhat literary or formal tone. It is more emphatic than simply using いちばん一番 or もっとも最も, and it often appears in written language, news articles, introductions, and speeches. It implies that the person or thing stands out unquestionably as the best or most notable within the given scope.
The scope noun is typically a place, organization, or group:
きっての is a fixed expression and does not conjugate or change form. It always appears as Noun + きっての + Noun.