  A solution of Einstein's vacuum field equation is derived that describes a
general boosted Kerr black hole relative to a Lorentz frame at future null
infinity. The metric contains five independent parameters -- mass $m$, rotation
$\omega$, boost parameter $v/c$ and the boost direction defined by
$(n_1,n_2,n_3)$ satisfying $(n_1)^2+(n_2)^2+(n_3)^2=1$ -- and reduces to the
Kerr black hole when the boost parameter is zero and $n_1=1$. The solution
describes the most general configuration that an astrophysical black hole must
have. The black hole rotates about the $z$-axis with angular momentum
proportional to $m \omega$ and the geometry has just one Killing vector
$\partial/\partial{u}$, where $u$ is the retarded time coordinate. The boost
turns the ergosphere asymmetric, with dominant lobes in the direction opposite
to the boost. The event and Cauchy horizons, defined for the case $\omega < m$,
are specified respectively by the radii $r_{\pm}=m \pm \sqrt{m^2-\omega^2}$.
The horizons are topologically spherical and the singularity has the topology
of a circle on planes that are orthogonal to the boost direction. We argue that
this black hole geometry is the natural set to describe the remnants of the
recently observed gravitational wave events $GW150914$, $GW151226$, $GW170814$
and $GW170817$\cite{gw1,gw2,gw3,gw4}. In the conclusions we discuss possible
astrophysical processes in the asymmetric ergosphere and the electromagnetic
dynamical effects that may result from the rotating black hole moving at
relativistic speeds together with the precession of the boost axis about the
rotation axis of the black hole.
