Gilgamesh Wulfenbach/Mad

Gil's Mother
It is assumed that Gil's mother is the  to whom Klaus refers only once in the first eight volumes. One popular theory is that Gil's mother is Zantabraxus, Warrior Queen of Skifander. See below.

Skifander Connection
It is widely suspected that Lucrezia sent Klaus to Skifander roughly 22 years ago. This would explain why Klaus can speak Skif.

Wherever Klaus was for those 4-5 years would include Gil's birthplace (or at least include his meeting the woman who would give birth to Gil). Further, Klaus thinks that a green-haired woman who speaks Skif, that is, some one from Skifander, would have reason to kill Gil.

Baron Wulfenbach's statement that he "kept [Gil] alive" hints at the old story that Amazons (to whom the tribeswomen of Skifander bear more than a passing resemblance) kill all of their male children. Whether this is accurate, of course, would be known only to Zeetha, to whom the question has not yet been put.

See also: Forum:Gil's mother

Relationship to Zeetha
It is speculated that the Chump of whom Zeetha is a daughter could be Klaus Wulfenbach, which would make Gil her brother. This may be foreshadowing of that possibility or merely the Foglios teasing us.

Gilgamonster
What did Klaus do to alter Gil to make him respond to ? Is Gil already a construct? What will be the of the Battle-Draught that Gil took? Will he develop some Jägermonster-like characteristics?

Battle-Draught (which heals Jägers) is, one hopes, distinct from the Jägerbräu (which creates them). There has been some suggestion outside the main narrative that taking Jägerbräu is dangerous (i.e., a fairly high percentage of subjects die immediately), which is further reason to believe that they are distinct.

Is today's story, 22-05-09, pruf Gil has Jäger characteriztiks? Dot vas very Jäger-like battle-rage.

SEP
The ability of the Baron to hide Gil's sonship and his spark, that Bang (and especially Vole?) underestimate him, and that members of the Storm King & Lady Heterodyne conspiracy remain unaware of him until too late seem consistent with the Somebody Else's Problem effect. It may be that Klaus managed to to create a SEP field generator.

Gil Dies
According to Othar's Twitter (which is considered Canon, but extremely unreliable), Gil inside Castle Heterodyne. Of course, it could be an alternate timeline, a dream sequence, a reference to some future visit to Castle Heterodyne years from Volume 9, a deception fostered by Gil, or an error by witnesses. If it's something like that, one possibility that it suggests that Agatha's the time travel device  is coming up before they leave Castle Heterodyne.