|Jacob Anton Ness|
|Cause of death:||
Killed by Theodore "T-Bag" Bagwell
Using the alias Poseidon, Jacob is the leader of 21 Void. He is involved with Michael Scofield's incarceration in Ogygia Prison; A&W and Van Gogh are under Poseidon's employ. Poseidon is a rogue CIA operative who pursues his own agenda.
Poseidon sent Michael to Ogygia to break out Abu Ramal. Prior to Michael's marriage to Sara, he was contacted by Poseidon to work for him. Michael refused to do so and Poseidon ended up having Sara imprisoned for Christina Scofield's death in order to force Michael to work for him. Michael faked his death and began breaking various criminals out of prison as part of the 21 Void.
Additionally, Poseidon framed Michael for the death of deputy CIA director Harlan Gaines. Jacob also recruited David Martin, the son of Theodore Bagwell, to help Michael at his request for the various mission. Jacob found several origami cranes in the mail with messages from Michael and dumped each one into the sewer to prevent him from contacting Sara.
Poseidon begins brainwashing Michael Jr. to believe that his mother is dead and Michael really is Kaniel Outis. Michael sets up a trap for Poseidon that results in the death of Whip, but ends in Michael recreating Harlan Gaines' death in order to reframe Poseidon for the murder along with Harlan's blood left by Michael in Poseidon's lair. Both Poseidon and Michael are arrested, but Lincoln Burrows captured one of Poseidon's associates while rescuing Michael Jr. With the evidence planted by Michael and the testimony of Poseidon's associate, Michael is exonerated for the murder and his real identity restored.
- Poseidon is the Greek god of the ocean.