Before the area known as Astro City was even known as Romeyn Falls, a musician traveled the country, playing music with a guitar whose strings were pure silver.
The man's background was unknown, leading to numerous tales about his origins, all drastically different: a runaway slave, a white shipwright's son, a Chinese railroad worker, a Mexican, a half-breed Indian. Accordingly, for lack of a more concrete name, he was called Silverstring on account of his musical instrument.
Wherever Silverstring traveled (and he never stopped traveling), he would play the songs he knew (or wrote) and learned new tunes from the locals. His travels allegedly took him not only across the country but to other lands and worlds, where he learned and shared the music of those realms' inhabitants as well.
Eventually, Silverstring found his way to Astro City, where he died. The details regarding how and why he died are just as varied as those of his background. When he died, his guitar broke or was torn apart by some unseen force, making an ungodly noise before catching fire. Its silver strings were said to twist about as though they were alive.
Silverstring's guitar was said to be magical--or at least to play magic--and keep away evils from those who were near. Many claimed that his magical music saved many lives that would otherwise have been lost.
It is strongly implied that the magic of Silverstring's instrument served to give birth to Mister Cakewalk and Jazzbaby (as evidenced by the silver treble clef shape that appeared before the initial arrival of either hero), meaning that Silverstring could well be the source of the Bouncing Beatnik or the Halcyon Hippie's existence as well.
Given that the Broken Man is also suspected to be connected to these heroes, then it is possible that the Broken Man's Dream House exists at the point along the Gaines River where Silverstring is shown to be buried.