Pigley III, the third iteration of Pigley
Pigley is Krieger's project. Dr. Krieger is known to do many unorthodox projects on ISIS's dime, and Pigley is one of those. Not much is known about the previous Pigleys. The current Pigley, Pigley III, was shown in "The Honeymooners" as what appeared to be a normal pig, just heavily irradiated. He also seems to enjoy eating human flesh.
Pigley I
Krieger having to put down Pigley I
Pigley is first mentioned in "Stage Two" as a half-human, half-pig hybrid, who is never shown on screen. In a flashback, Krieger is shown having to put down Pigley whilst saying: "That'll do Pigley, that'll do."
Pigley II
Krieger pocketing a pig.
Krieger had been shown hiding a piglet in his pocket during "Fugue and Riffs", it is unknown if that was Pigley II, or what would grow into Pigley III. It was shown dead in The Wind Cries Mary.
Pigley III
Pigley III eating the North Koreans
Pigley was shown pig experimented on by Krieger in "The Honeymooners", and possibly having a plutonium rod in his rectum, also Krieger's. Pigley glowed bright green, as if he had already been strongly irradiated. It is unsure if the plutonium rod is what Krieger was smuggling to the North Koreans, or if it was part of creating Pigley. At any rate, Pigley enjoys eating human flesh, which Krieger consents to, telling Pigley "God knows you've earned it".