  We present a multiple stellar population study of the metal-poor globular
cluster (GC) M92 (NGC 6341), which is long known for the substantial
metallicity dispersion, using our own photometric system. We find two groups
with slightly different mean metallicities, the metal-poor (MP) stars with
[Fe/H] = $-$2.412$\pm$0.03, while the metal-rich (MR) ones with
$-$2.282$\pm$0.002. The MP constitutes about 23\% of the total mass with a more
central concentration. Our populational tagging based on the [C/Fe] and [N/Fe]
provides the mean n(P):n(I):n(E) = 32.2:31.6:36.2 ($\pm$2.4), where P, I, and E
denote the primordial, intermediate, and extreme populations, respectively. Our
populational number ratio is consistent with those of others. However, the MP
has a significantly different populational number ratio than the mean value,
and the domination of the primordial population in the MP is consistent with
observations of Galactic GCs that less massive GCs contain larger fractions of
the primordial population. Structural and constituent differences between the
MP and MR may indicate that M92 is a merger remnant in a dwarf galaxy
environment, consistent with recent suggestions that M92 is a GC in a dwarf
galaxy or a remnant nucleus of the progenitor galaxy. Discrepancy between our
method and those widely used for the HST photometry exists in the primordial
population. Significant magnesium and oxygen depletions of $-$0.8 and $-$0.3
dex, respectively, and helium enhancement of $\Delta Y$ $\gtrsim$ 0.03 are
required to explain the presence of this abnormal primordial group. No clear
explanation is available with limited information of detailed elemental
abundances.
