51 Pegasi (abbreviated 51 Peg), formally named Helvetios /hɛlˈviːʃiəs/,[12] is a Sun-like star located 50.6 light-years (15.5 parsecs) from Earth in the constellation of Pegasus.

[3] It is generally considered to still be generating energy through the thermonuclear fusion of hydrogen at its core, but to be in a more evolved state than the Sun.

On its discovery, the star's planet — and actually the first exoplanet discovered around a main-sequence star — was designated 51 Pegasi b by its discoverers and unofficially dubbed Bellerophon, in keeping with the convention of naming planets after Greek and Roman mythological figures (Bellerophon was a figure from Greek mythology who rode the winged horse Pegasus).

[20] In July 2014, the International Astronomical Union launched NameExoWorlds, a process for giving proper names to certain exoplanets and their host stars.

[12] On October 6, 1995, Swiss astronomers Michel Mayor and Didier Queloz announced the discovery of an exoplanet orbiting 51 Pegasi.

At the time of its discovery, this close distance was not compatible with theories of planet formation and resulted in discussions of planetary migration.