  We present 44 days of high duty cycle, ultra precise photometry of the 13th
magnitude star Kepler-5 (KIC 8191672, Teff=6300 K, logg=4.1), which exhibits
periodic transits with a depth of 0.7%. Detailed modeling of the transit is
consistent with a planetary companion with an orbital period of
3.548460+/-0.000032 days and a radius of 1.431+/-0.050 Rj. Follow-up radial
velocity measurements with the Keck HIRES spectrograph on 9 separate nights
demonstrate that the planet is more than twice as massive as Jupiter with a
mass of 2.114+/-0.057 and a mean density of 0.894+/-0.079 g/cm^3.
