PSR B1620-26 is a millisecond pulsar in the globular cluster Messier 4. PSR B1620-26 b, the Methuselah planet, is among the oldest known worlds and orbits a pulsar–white-dwarf binary in the globular cluster Messier 4. PSR B1620-26 b is a 2.50-Jupiter-mass companion, at 23.0 AU from its star, discovered in 2003 via pulsar timing. PSR B1620-26 adds another data point to the growing catalogue of planetary systems whose masses, orbits, and host-star properties constrain models of planet formation. PSR B1620-26 b orbits far from its host star. The 2003 announcement placed PSR B1620-26 among the thousands of confirmed planetary systems mapped since the first exoplanet detections. Comparing systems like PSR B1620-26 with our Solar System tests theories of planet formation, migration, and long-term orbital stability.