Step 1: The question is about the inner world of the character in the poem "The Sleeping Porter."
Step 2: The poem contrasts the porter's harsh, impoverished reality with his rich, imaginative inner life.
Step 3: While awake, the porter is a poor laborer. However, when he is asleep, he escapes his reality. In his dreams, he is a king, rich and powerful. Therefore, he is "reigning over the kingdom of sleep," where he finds freedom and solace that his waking life denies him.