Fallen Hero

Fallen Hero is a miscellaneous quest given to you by Joe Savoldi, owner of the bar at Bunker Hill.

Detailed walkthrough
Find Joe Savoldi in Bunker Hill most likely at his bar/motel on the West side. When you first speak to him he may go into dialogue with his son and bring you in to it. Keep talking to him until the job dialogue option is available then select it and he'll tell you about his grandfather being in the minutemen.

You'll be told to find any trace of him. You can find his remains at the bottom of the Old Gullet Sinkhole north of Bunker Hill. In order to find Savoldi's body, you'll have to jump into the swirling water at the bottom. Once you enter the sink hole, you'll end up in a cave below that contains one glowing and one normal radroach. Pick up his grandfather's hat and the copy of the Wasteland_Survival_Guide_(Fallout_4) opposite him and proceed to head out through the tunnel you'll encounter a legendary ghoul along with a few regular ghouls on your way out.

The cave sits below, and exits to, a house just west of the sinkhole. You may get a random spawning of the BOS fighting a Deathclaw after exiting the house.

Return to Bunker Hill and give the hat to Joe and he'll reward you with 150 bottle caps. If you have joined the Minutemen, he will also let you keep the hat.