The Dark Star was once dug up by the citizens of Toad Town a very long time ago. It was proven to be a deadly and vicious threat that required the help of the Star Sprites to defeat it by keeping it sealed away.
However, Fawful got his hands on the Dark Star's seal after gaining all the essential resources needed for his plan of world domination. The Dark Star was eventually awoken after Bowser defeated Midbus for the final time. Fawful attempted to absorb the demonic star's power, but the process was interrupted, since Bowser punched Fawful away from the Dark Star. It then infiltrates Bowser's body and takes some DNA samples for itself to achieve a more powerful form.
After Mario and Luigi defeat it in battle, the Dark Star fled Bowser's body and became a shadowy doppleganger of Bowser. However, it lacked the sufficient power to complete it's transformation, and sought Fawful to complete it's unfinished form.
After Fawful is defeated by Bowser, the Dark Star inhales Fawful to complete it's transformation, thus, becoming Dark Bowser. Bowser pursues his doppleganger to the summit of Peach's Castle for the final battle, while Mario and Luigi would back him up in the process. In the end, Bowser emerged victorious after defeating Dark Bowser with a barrage of punches. Dark Bowser reverts to it's original form and explodes in the sky, bringing peace to the Mushroom Kingdom once more.
The Dark Star has received mixed to positive reception by fans of the Mario & Luigi series. The Dark Star holds a reputation as being one of the most fearsome villains in the Mario series.
Although it lacks some personality, aside from harboring pure hatred and malice, the Dark Star is admired by some fans for being another great foil to Bowser in it's Dark Bowser persona.