Here the speaker is a sun, or a figure who once believed himself one, looking back on a time of absolute power. He calls himself the Sun King and boasts that shadows spread out from him like the teeth of defeated enemies strung into a necklace. He even claims to have been "the state." The imagery is grand, violent and a little ridiculous, which fits the title's hint of a mock ruler.
The tone shifts as the poem goes on. Now he must "perform / for the forgotten and forgettable," and he wonders why he hasn't simply drifted into the clouds and faded. Instead he is stuck with a "legacy of lead" and asteroids roaring inside a "farcical heart." The mood is bitter, self-mocking and restless: pride has turned into embarrassment. The poem seems to picture power that has outlived its meaning, and a speaker who can see his own absurdity but can't escape it.