  We present the first detection of the mass donor star in the cataclysmic
variable WZ Sge. Phase resolved spectroscopy reveals narrow Balmer emission
components from the irradiated secondary star during the 2001 outburst. Its
radial velocity curve indicates a systemic velocity of -72 +/- 3 km/s and an
apparent velocity amplitude of K_2_app=493 +/- 10 km/s. Doppler tomography
reveals a highly asymmetric accretion disc including a significant bright spot
contribution 20 days into the outburst. We estimate the primary radial velocity
K_1 using a center of symmetry method and find K_1_app=37 +/- 5 km/s.
Accounting for the likely systematic errors affecting both K_1 and K_2
measurements, we conservatively derive 508 < K_2 < 585 km/s and K_1 < 37 km/s.
This implies a massive white dwarf with M_1 > 0.77 M_sun. A non-degenerate mass
donor, implying WZ Sge has not yet evolved through its minimum orbital period,
is not ruled out by our observations. This would require an improved estimate
of K_1. Together with the measured phase offset between bright spot eclipse and
inferior conjuction of the secondary star, we can bracket the allowed mass
ratio (q=M_2/M_1) to lie between 0.040 and 0.073. This provides a firm upper
limit to the mass of the secondary of M_2 < 0.10 M_sun.
