Jesse Alexander was part of a secret covert black ops division of the Nova Corps, at home on Earth, Jesse would tell his children stories of his adventure out in space. As a Nova Centurion, Jesse was tasked to protect Warlock and destroy him should he ever turn evil. One day their ship was attacked by Thanos who came after Warlock (in his cocoon form) on board, Jesse the last surviving Nova faced against Thanos with all he had but was defeated when Thano slammed his head to the ground and was supposedly killed. Thanos took Warlock's cocoon a well as Jesse's Nova helmet (that was damaged in the fight) and placed them in a sarcophagus on Sanctuary.
Long after Thanos was defeated by the Guardians of the Galaxyand his Sanctuary destroyed, the Guardians were able recover the sarcophagus and find Jesse's damaged helmet, with it they discovered the existence of the Nova Centurions. The helmet was later confiscated by the Nova Corps.
When Warlock emerged from his cocoon, Jesse's helmet started acting wild and broke out of it's containment into Titus' prison cell, that he used to escape. After Warlock fully matured, he fixed the helmet and sent out to "find its destiny".
The helmet arrived at the garage of Jesse's old home where his son Sam Alexander found it, upon wearing it Sam finds a recorded hologram message from his father telling him not to try and search for him, ignoring this Sam uses the helmet to find him.