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ROSAT, ASCA, RXTE and now Chandra X-ray observations of the supermassive star η Carinae obtained over the past 7 years chronicle the inordinate variability of the high-energy emission. The most important characteristics are these: 1) the hard X-ray “low state” evidently recurs with a period consistent with the “Damineli Cycle” of 5.5 years; 2) the X-ray emission exhibits “flares” which occur quasi-periodically; 3) the overall X-ray brightness in the current “cycle” is brighter than at the same phase in the last cycle; 4) the hard, variable “core” source is apparently resolvable at lower energies but unresolvable at energies above ∼4 keV. The X-ray data appear consistent with a model of X-ray generation via colliding winds in a massive binary system coupled with dust scattering, though the “flaring” activity probably requires that the wind from at least one of the stars is azimuthally structured. It is difficult to account for all the X-ray properties by activity in a single star. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]