Knightle was first introduced as one of the witnesses during the first witch trial. He provided various statements, but got depressed when Phoenix Wright exposed the contradictions. The following day, he overslept for his knight entrance exam, causing him to fail. This caused him to abandon the dream of becoming a knight, and started selling potatoes instead, calling himself "Spudley".
Shortly after Phoenix Wright and Luke find him on the market, an explosion happens, destroying his potato cart, making him give up on selling potatoes as well. Luke suggests to him that he take yet another temporary name, so Knightle then calls himself Whatley until he can find a new job.
Spoilers end here