Manjushri
stands for the
highest
Enlightment-
aspects of
transcendental
wisdom which should
be used to free
oneself from karmic
bondages (his symbols:
book and sword). He is
also the main patron
of astrology and
medicine and
 an emanation of the
water element.
The snow-lion,
on which he rides,
symbolizes
the overcoming
of the ego. His
most famous mantra
is: OM AH RA PA
TZA NA DHI 
Seed syllable: DHI