an examination of theon greyjoy's feelings about and (implied) relationship with evil uncle euron
Theon searched for his uncle Euron's Silence. Of that lean and terrible red ship he saw no sign, but his father's Great Kraken was there, her bow ornamented with a grey iron ram in the shape of its namesake.
[...] It might be only a caution, now that he thought on it. A defensive move, lest the war spill out across the sea. Old men were cautious by nature. His father was old now, and so too his uncle Victarion, who commanded the Iron Fleet. His uncle Euron was a different song, to be sure, but the Silence did not seem to be in port. It's all for the good, Theon told himself. This way, I shall be able to strike all the more quickly. -Theon I, aCoK
the first we read of euron is in theon's first pov as he searched the harbor at lordsport for euron's ship. no reason is given for singling that ship out nor an initial reaction to its absence. later down the page euron is described as different from balon and victarion, with none of an older man's caution to be expected from him. that's why theon thought it for the best that euron's ship was not in port, though at this point it appears his only concern is being the boldest greyjoy around, commanding the fleet all the more quickly for its already being assembled, and not being outshone by euron. the only hint at more is his description of the ship as "terrible".
"You can marry off your sister," Esgred[Asha] observed, "but not your uncles."
"My uncles . . ." Theon's claim took precedence over those of his father's three brothers, but the woman had touched on a sore point nonetheless. In the islands it was scarce unheard of for a strong, ambitious uncle to dispossess a weak nephew of his rights, and usually murder him in the bargain. But I am not weak, Theon told himself, and I mean to be stronger yet by the time my father dies. [...]
[Asha-as-Esgred, to Theon:] "Euron Croweye has no lack of cunning, though. I've heard men say terrible things of that one."
Theon shifted his seat. "My uncle Euron has not been seen in the islands for close on two years. He may be dead." If so, it might be for the best. Lord Balon's eldest brother had never given up the Old Way, even for a day. His Silence, with its black sails and dark red hull, was infamous in every port from Ibben to Asshai, it was said. -Theon II, aCoK
by theon's next chapter, when he and (unknown, to him) asha discuss their greyjoy uncles, theon has learned that euron hasn't been seen in the iron islands for two years. atp, rather than just noting that euron's not at home, theon has decided it's for the best if he's died somewhere and can never return. the word terrible is again used wrt euron and it's also said that his ship is infamous all over the world. euron is the only greyjoy never to have given up the old way in any sense, and the implied danger to theon is that he could also partake in the old tradition of a strong, ambitious uncle murdering his nephew. euron has thus been establishled as a villain, a threat, and possible kinslayer more specifically but we have yet to learn all the other, more unique aspects of his villainy. i think it likely that grrm, with his gardener-writing, had not yet decided that euron was an incestuous sexual predator. the risk of nepoticide is enough to explain theon's nervous shifting at the mention of euron's cunning and the terrible things said of him, but it could also apply to euron's full characterization only revealed years later in aeron's pov, one of those little half-open seeds gardener-grrm could decide to grow later.
[Robb Stark, to his assembled bannermen and his mother:] "Euron Greyjoy is no man's notion of a king, if half of what Theon said of him was true. Theon is the rightful heir, unless he's dead . . . but Victarion commands the Iron Fleet. I can't believe he would remain at Moat Cailin while Euron Crow's Eye holds the Seastone Chair. He has to go back." -Catelyn V, aSoS
our next clue about theon/euron is not from his own pov but in the book between his arcs when he's "offscreen". i'd say the fact that theon had confided to robb at all about euron is significant, let alone that he related enough things about euron for robb to rhetorically dismiss half of what theon told him and still feel confident of ironborn infighting with euron on the throne. (with theon's status unknown and asha absent from the isles too, euron would have a claim to that throne and a better one than victarion regardless as the eldest surviving greyjoy. vic is the dutiful younger brother who wouldn't normally make any power play, so for robb to know that euron's rule would be challenged by his younger brothers shows he does indeed have insider intel wrt euron.)
this accurate read from robb stands in pretty, ahem, stark contrast to everything theon must have told robb and himself about the likelihood of a robb/balon alliance. an impartial observer who knew (as theon did) that balon's first rebellion was about bringing back the old way more than just independance from the iron throne would have known those goals were not in line with the kitn's cause and that alliance was a no-go from the start. we see in the quoted portion of theon i above how he lied to himself about balon becoming a cautious old man and this being his time in the sun, yet it seems euron was the one family member he couldn't lie to himself about. not only did euron make such an impression on him that theon always remembered him very clearly but the effect was such that amid all his hostage time at wf fantasizing about his return home, he felt the need to tell robb the truth about this one scary relative by confiding in him with multiple stories. (though if euron had sexually abused theon, i can't imagine him ever explicitly revealing that to robb or anyone else.)
"My uncle[Victarion] is never coming back," Reek told them[the ironmen Victarion abandoned at Moat Cailin]. "The kingsmoot crowned his brother Euron, and the Crow's Eye has other wars to fight. You think my uncle values you? He doesn't. You are the ones he left behind to die. He scraped you off the same way he scrapes mud off his boots when he wades ashore." -Reek(/Theon) II, aDwD
this is euron's only name-drop in theon's dance pov, significant only in that it shows theon had recent news of his uncles, enough to know that euron dgaf about keeping balon's northern conquests and had instead drawn vic and the other captains far away. which brings me to ...
Crowfood. Theon remembered. An old man, huge and powerful, with a ruddy face and a shaggy white beard. He had been seated on a garron, clad in the pelt of a gigantic snow bear, its head his hood. Under it he wore a stained white leather eye patch that reminded Theon of his uncle Euron. He'd wanted to rip it off Umber's face, to make certain that underneath was only an empty socket, not a black eye shining with malice. Instead he had whimpered [...] -Theon I, tWoW
here, we have theon meeting a non-bolton northman he's known before, no different really from all the non-bolton northmen inside wf or any others he'd met growing up there, none of whom really seemed to scare him as his captors did, yet the mere sight of mors "crowfood" umber's eye patch is enough to freak theon the fuck out, wanting to rip off the eye patch for reassurance that crowfood was just a regular guy. this is the kind of terror we'd expect wrt ramsay, which would make sense in that regard, as ramsay had been his most immediate abuser, torturing theon in every sense for around a year almost right up until the moment of his escape, and ramsay's still right there in wf, so theon had good reason to still fear recapture by him. euron, though? that's an uncle he hadn't seen in over ten years, who theon knew to be far from wf as seen in the above dance quote, so he had no reason to expect to see him again in that part of westeros and one would think he had enough immediate problems not to worry about someone he hadn't seen in so long. you'd think his pre-ned, pre-ramsay childhood with all the greyjoys would feel a lifetime away with all he'd been through since, esp the reekening. but whatever impression euron left on him was still just as clear and fresh as ever, so that anyone with an eye patch could suddenly make him feel fear of an uncle hundreds of miles and a decade removed from him. from this moment i take away two things: 1) theon will survive stannis and have to meet uncle euron again bc otherwise i don't see the point of grrm throwing this in here and 2) it now feels a helluva lot more likely that theon was another csa victim of euron's bc i don't think this kind of sudden fear could be accounted for with just general scariness from euron. feels more like being triggered by a trauma flashback (just as aeron had as soon as he heard that euron had taken balon's throne), doesn't it?
after all, theon/aeron are already linked in the feastdance as both are youngest greyjoy siblings who happen to also be victims of abuse who had buried their old selves in a new identity. aeron's old self even sounds a lot like pre-ramsay theon. theon remembered pre-born-again aeron as the "most amiable of his uncles, feckless and quick to laugh, fond of songs, ale, and women", and aeron described his younger self as "a sack of wine with legs. He would sing, he would dance [...] he would jape and jabber and make mock. He played the pipes, he juggled, he rode horses and could drink more than all the Wynches and the Botleys, and half the Harlaws too." doesn't that sound like the ever-smiling and joking unserious theon we first met, fond of wine and womanizing, once a good dancer, and better ahorse than most ironborn? the only part really missing for theon is aeron's ability to always win literal pissing contests. you'd think being sexually abused by two different evildoers (euron and ramsay) would be enough of a parallel, but this winds preview chapter certainly makes it seem like they also shared the specific experience of being abused by euron in childhood too. our poor youngest kraken really did never have a chance, did he?