Perhaps you are a
The giveaway (if this is right) was actually Tom's comment that
"an anagram of the answer gives someone who could be a Knight from the relevant country"
because that suggested
looking for anagrams of SIR POLE.
Anyway, here are explanations of the verses (some with thanks to Tom for providing pointers in comments to things I'd missed; I'm leaving in my own half-baked thoughts even where they were wrong).
More than surprising,
and slippery to the core,
I give resistance.
A spoiler gives away the otherwise surprising plot of a book or movie. At the centre of "spoiler" we find oil, which is slippery. A spoiler on a car provides resistance to airflow and hence turbulent rather than laminar flow in a particular region, which reduces overall drag by some means I don't understand. Edited to add: OP indicates that I'm misunderstanding the first line and need to "translate symbolically", and after further prodding I finally get it: it's a reference to the SO markup for spoilers,
> is "more than" and
! is "surprising".
I hide my secrets,
until you come upon me,
This would apply pretty well to book/movie spoilers, but I think it's actually referring to the spoiler-hiding mechanism we have here. Spoilering a paragraph like this one you're reading right now hides its secrets but when you move your cursor over it it reveals itself.
Evening stars of,
Currently baffled by this. Does "transcendental" refer to transcendental numbers? (See the sixth verse, below.) Perhaps -- though this is rather a stretch -- we're taking the middle of Hesperus (Venus as the "evening star") and inserting "oil" (as in an illuminating oil lamp) to yield SPOILER. But what's transcendental about that? And why "evening stars", plural, in that case? And why only the middle of "Hesperus"? I think it's just coincidence that this construction works. Edited to add: yes, it's coincidence; OP's intention was that "evening stars" indicates evenly spaced letters: SPOILER yielding PI and E or $\pi$ and $e$, both transcendental.
centrally coiled hemisphere,
SPOILER is almost an anagram of (found by unravelling) the central letters of "coiled" and "hemisphere". Perhaps "centrally" is referring to itself too, which would give us the missing "r". Edited to add: OP indicates that the actual intention was OILE from "centrally coiled" plus SPR from "hemisphere" (i.e., half of SPHERE).
The source of gold eggs,
sifting sibilant language,
giving birth to me.
Currently baffled by this. The story of the goose that laid golden eggs is first found in Aesop, whose name has a lot of letters in common with SPOILER, but I don't see how to do anything useful with that. And "goose" in French is "oie" which also has a lot of letters in common with SPOILER, but I don't see what to do with that either. Edited to add: OP indicates that "a source of gold or eggs" might have been a better L1 and that we're looking for a computer language here, and after a bit more prompting from OP because I was stupid this is of course ORE/ROE plus LISP.
I'm from the third sphere,
said the Swiss eponymous,
for my sixth one.
Sixth letter is E, so maybe this is a reference to the transcendental number e, named for the Swiss mathematician Euler. Not sure about the "third sphere"; perhaps there's some fanciful remark Euler made about e. (I guess it's the third celestial sphere, though what that is depends on whose geocentric model you use and whether you count from the inside or the outside.) Edited to add: nope, that's all wrong; OP indicates that actually "the third sphere" = 1/3 of SPHERE = SP, plus "said the Swiss eponymous" = sounds-like a Swiss person after whom things are named = sounds-like Euler = OILER.