Wally Prysin is one of Varrock's most famous heroes. When the powerful demon Delrith attempted to destroy the city, Wally narrowly managed to defeat him with the sword Silverlight in the 19th year of the Fifth Age, 150 years ago. He died sometime after, and has since been forgotten by many. He is the father of Waldo.
Wally wielding the enchanted sword Silverlight in the old version of Demon Slayer.
Wally's helmet, which he is said to have worn when he battled Delrith, is displayed at the Outpost near Ardougne after completion of the Making History quest. During the old version of Demon Slayer, when a cutscene showed Wally defeat Delrith, he was not wearing a helmet. This was most likely just an error by Jagex.
Originally, Wally did not appear in any cutscenes and was only mentioned by Gypsy Aris and Sir Prysin. Since the rework of the quest, he does not appear once again.
Although Wally was visible in a cutscene during the Demon Slayer quest, he had no examine option, likely due to him actually being a reskinned version of the player.