  We present the 0.85-2.5-micron discovery spectrum and multi-epoch photometry
of the new high-redshift quasar ULAS J081621.47+213442.6 obtained using the
GNIRS spectrograph of the Gemini North and near-infrared wide-field camera of
the 4-m UKIRT telescopes. The redshift of ULAS J081621.47+213442.6 measured
from the MgII 2799 emission line is z=7.461. The absolute magnitude of the
quasar is M1450=-25.33. The black hole mass estimated using the MgII 2799 line
and Eddington accretion rate are ~5x10^8Msun and ~0.7. The spectrum of ULAS
J081621.47+213442.6 exhibits strong NIII] 1750 emission line of a rest-frame
equivalent width of ~12.5 A. The high abundance of nitrogen suggests that ULAS
J081621.47+213442.6 may be at the peak of the nitrogen enrichment of the
circumnuclear region by the asymptotic giant branch stars, which is expected
~0.25 Gyr after the bulk of star formation. The age of the starburst of ULAS
J081621.47+213442.6 implied by the high nitrogen abundance, indicates that the
active phase of the black hole growth of the quasar may have lasted only ~0.25
Gyr, favoring a massive initial black hole seed. We also observed the flux
variations of the UV continuum of ULAS J081621.47+213442.6 caused by the
variation in the line-of-sight absorbing column density on a rest-frame
timescale of ~47 d. The estimated hydrogen column density of the gas cloud
responsible for this variation is N~10^{23.5} cm^{-2}, consistent with the
typical column density of mostly neutral, gravitationally bound clouds of the
broad line region of quasars.
