Historical source for Faust figure Valentin?

A historical figure is certainly not Valentin. He has been thought of by Goethe in a poetic way to expand and deepen the dramatism/tragik Gretchens by wanting her brother Valentin to avenge his sister’s “conductor” and killing himself with the help of the devil Mephisto by Faust. Gretchen therefore not only loses her mother (by the “sleep drink” given to her) and her child (they kill it knownly), but also her bodice and venerable brother Valentin. Their own destiny (direction) can thus be experienced even more in the seal.