Which star was the first Sun-like star known to have a multiplanet exoplanet system?

Upsilon Andromedae was the first Sun-like star known to have a multiplanet exoplanet system.

Astronomers announced the system in 1999 after radial-velocity measurements detected three planets orbiting Upsilon Andromedae A, a roughly Sun-like main-sequence star in the constellation Andromeda. The discovery showed that planetary systems around ordinary stars could be much more complex than the Solar System then known.

The planets were designated Upsilon Andromedae b, c, and d. Their orbits are notably unlike the nearly circular, mostly coplanar orbits of the major Solar System planets: the outer planets have substantially eccentric paths, and later studies found that the system is influenced by a stellar companion.

A common mix-up is confusing “first multiplanet system” with the first exoplanet discovery overall. 51 Pegasi b was the first confirmed planet found around a Sun-like star, in 1995, but Upsilon Andromedae was the first such star shown to host multiple planets.