These are the “famous” people with whom I have had one-on-one meetings or discussions and only in private, never in public. Some meetings were for up to an hour, and many I met with more than once, all one-on-one:
In alphabetical order, lest anyone be offended:
Rav Ben Zion Abba Shaul
Rav Shlomo Zalman Auerbach
Rav Yosef Elyashiv
Rav Shneur Kotler
Rav Yitzchak Ruderman
Rav Eliezer Menachem Man Schach
Rav Yosef Dov Soloveitchik
Rav Yitzchak Yaakov Weiss (the Minchas Yitzchak)
Rav Eliezer Waldenberg (the Tzitz Eliezer)