Your Dragon
My best friend and I have a joke about his ex girlfriend, and we call her a 'Dragon.' So for us, the term 'Dragon' has become that threat to your life, or something that has hurt you or held you back that became an emotional obstacle, and by slaying the Dragon you in turn become stronger, whether it's physical, emotional, or anything else.
So what is your Dragon? What is the beast that took you to your fullest to slay and move on? My Dragon was the vicious beast known as 'Lack of Self-Confidence,' or 'Low Self-Esteem.'