  Based on two decades of radial velocity (RV) observations using Keck/HIRES
and McDonald/Tull, and more recent observations using the Automated Planet
Finder, we found that the nearby star HR 5183 (HD 120066) hosts a 3$M_J$
minimum mass planet with an orbital period of $74^{+43}_{-22}$ years. The orbit
is highly eccentric (e$\simeq$0.84), shuttling the planet from within the orbit
of Jupiter to beyond the orbit of Neptune. Our careful survey design enabled
high cadence observations before, during, and after the planet's periastron
passage, yielding precise orbital parameter constraints. We searched for
stellar or planetary companions that could have excited the planet's
eccentricity, but found no candidates, potentially implying that the perturber
was ejected from the system. We did identify a bound stellar companion more
than 15,000 au from the primary, but reasoned that it is currently too widely
separated to have an appreciable effect on HR 5183 b. Because HR 5183 b's wide
orbit takes it more than 30 au (1") from its star, we also explored the
potential of complimentary studies with direct imaging or stellar astrometry.
We found that a Gaia detection is very likely, and that imaging at 10 $\mu$m is
a promising avenue. This discovery highlights the value of long-baseline RV
surveys for discovering and characterizing long-period, eccentric Jovian
planets. This population may offer important insights into the dynamical
evolution of planetary systems containing multiple massive planets.
