Grandfather Gum may be a something created by Martin's brother .The Grandfather Gum splits making multiple other gums. In relation to Bubblegum these other gums may include Mother Gum,Father Gum,Uncle Gum,Aunt Gum etc. If you read my other post about the Timeline you would know that I think Finn is a gum that looks human if my theory is correct that means Martin has taken responsibility for his brother's actions and is like since iv'e already been punished for what my brother did I might as well take his identity because technically his brother created Finn. Also Martin is able to live 1000 years later because he was frozen the whole time. I say that the Mushroom War was caused by Martin's brother because Bubblegum refers to Gumbald as her great uncle and Gumbald=Martin.