Longinus is the Roman soldier traditionally linked to the Holy Grail legend through the spear that pierced Jesus.
The connection comes from later Christian and medieval traditions surrounding the Passion of Christ. In the Gospel of John, an unnamed Roman soldier pierces Jesus’s side with a spear after his death. Christian tradition later gives this soldier the name Longinus, although the biblical text does not name him.
Grail romances developed additional sacred relic traditions around objects associated with the Passion. Some versions connect the spear of Longinus with the vessel used to collect Christ’s blood, while others distinguish the spear from the Grail itself. This is why Longinus appears in Grail-related legends without being the Grail’s owner or guardian.
A common mix-up is identifying Longinus as the person who brought the Grail to Britain. That role is more commonly assigned to Joseph of Arimathea in later medieval tradition, whereas Longinus is primarily associated with the Passion spear.