Contemporary leaders must prove themselves to Am Yisroel before we recognize them as a Gadol b'Yisroel. They must have excellent character as well as excellent scholarship.
An interesting example is Rav Moshe Feinstein zt”l, who permitted many women to remarry on the basis that their husbands perished in concentration camps. To this day, none of the men whom he pronounced dead was later discovered to be alive. A Posek and Gadol can also prove themselves by demonstrating their fidelity to Toras Moshe and their competence in Torah teachings and rulings to the point when the committed portion of the nation regards him as a Gadol, as they regarded Shmuel in the days of Sefer Shmuel.
The process of identifying an authentic Navi serves a model for identifying legitimate Torah leadership in all generations. It also parallels the manner in which we shall soon identify Moshiach (as described in the Rambam Hilchos Melachim 11:4). An authentic Jewish leader does not deviate from the teachings of Moshe Rabbeinu one iota. A legitimate Torah leader does not seek to change halachah but rather guides Am Yisroel how to properly observe the Torah in the midst of the many challenges that individuals and communities encounter in every generation.
