The Duke of Soleanna (ソレアナ王,Soreana-ō?, lit. "King of Soleanna") is a character in Sonic the Hedgehog (2006), voiced by David Wills in the English dub and by Kenji Utsumi in the Japanese dub. He was the father of Princess Elise. As the Duke is already dead at the time of the game's storyline, he only appears a few times: once when Shadow and Silver travel back in time to observe the Solaris Project firsthand, once in Elise's flashback during the cutscene following the Tropical Jungle stage, and once at the end of the game, when he and young Elise are viewing Solaris in his early form - the Flame of Hope - before Sonic and the present-day Elise extinguish him.
Following the death of Elise's mother, the Duke resolved to use the power of Solaris, the sun god honored by the citizens of Soleanna, to travel through time and see her again, as well as give humanity the chance to correct its past sins. However, the project became unstable when a device they were using exploded, and Solaris split into two villainous entities: Iblis, the raw power, and Mephiles, the conscious mind. The Duke was gravely wounded in the blast while attempting to protect Elise. Upon the arrival of a time-traveling Shadow and Silver, they both split up to pursue and capture Mephiles and Iblis respectively. The Duke, strangely not surprised to see them, gives Shadow the Scepter of Darkness in order to imprison Mephiles.
Once Silver has caught up to Iblis and psychokinetically paralyzed him, the Duke arrives with Elise. Silver shouts at him to leave, but the Duke replies that it is his duty to ensure that Iblis is not released into the world. With no other option, the Duke uses a Chaos Emerald to seal Iblis within Elise's soul during a ritual. When he is successful, he entrusts Silver to take Elise to a safe place, and, while lovingly stroking his daughter's hair, tells her to remain strong and not to cry under any circumstances, as Iblis would be set free if that were to happen. The Duke then dies, leaving Silver alone in the room with an unconscious Elise in his arms.
Due to the actions of Sonic and Elise in the past, which resulted in the permanent destruction of Solaris, it is possible that the Duke either died from another cause, or he may never have died at all. As he was not seen during the game's ending, his exact fate is uncertain.
The "voice" of the Hint Rings in the game could possibly be the spirit of the Duke interacting with the living world (much like Tikal), as the voice sounds suspiciously similar to his voice.
The Duke's use of a Chaos Emerald is the only direct use of a Chaos Emerald by any human so far. Though his daughter used all seven Chaos Emeralds to revive Sonic, she was able to transfer the power of the Chaos Emeralds into Sonic and create a 'miracle'.