The jailkeeper is ignorance
Gautama felt as though a prison which had confined him for thousands of lifetimes had broken open. Ignorance had been the jailkeeper. Because of ignorance, his mind had been obscured, just like the moon and stars hidden by the storm clouds. Clouded by endless waves of deluded thoughts, the mind had falsely divided reality into subject and object, self and others, existence and non-existence, birth and death, and from these discriminations arose wrong views—the prisons of feelings, craving, grasping, and becoming. The suffering of birth, old age, sickness, and death only made the prison walls thicker. The only thing to do was to seize the jailkeeper and see his true face. The jailkeeper was ignorance. And the means to overcome ignorance were the Noble Eightfold Path. Once the jailkeeper was gone, the jail would disappear and never be rebuilt again.
The hermit Gautama smiled, and whispered to himself, “O jailer, I see you now. How many lifetimes have you confined me in the prisons of birth and death? But now I see your face clearly, and from now on you can build no more prisons around me, you shall build no house (for me) again. How can you? I have destroyed the very materials by which you build it. All your rafters are broken, your roof-tree is destroyed. My mind has reached the unconditioned (i.e., Nibbana); the end of craving (Arahatta Phala) has been attained. And I am eternally awake.
– Dharmacakrapravartana Sūtra