  Aims: We investigate the physical nature of the X-ray emitting source 1RXS
J165443.5-191620 through optical photometry and time-resolved spectroscopy.
Methods: Optical photometry is obtained from a variety of telescopes all over
the world spanning about 27 days. Additionally, time-resolved spectroscopy is
obtained from the MDM observatory. Results: The optical photometry clearly
displays modulations consistent with those observed in magnetic cataclysmic
variables: a low-frequency signal interpreted as the orbital period, a
high-frequency signal interpreted as the white dwarf spin period, and an
orbital sideband modulation. Our findings and interpretations are further
confirmed through optical, time-resolved, spectroscopy that displays H-alpha
radial velocity shifts modulated on the binary orbital period. Conclusion: We
confirm the true nature of 1RXS J165443.5-191620 as an intermediate polar with
a spin period of 546 seconds and an orbital period of 3.7 hours. In particular,
1RXS J165443.5-191620 is part of a growing subset of intermediate polars, all
displaying hard X-ray emission above 15keV, white dwarf spin periods below 30
minutes, and spin-to-orbital ratios below 0.1.
