There are different accounts as to who created the secp256k1 standard, for example:
Mastering Bitcoin, p.61:
Bitcoin uses a specific elliptic curve and set of mathematical constants, as defined in a standard called secp256k1, established by the National Institute of Standards and Technology (NIST)
theymos in this thread on r/crypto:
secp256k1 isn't a NIST curve. It was created purely by SECG. SECG also publishes some NIST curves in their standards (such as secp256r1, aka P-256), but secp256k1 isn't one of them.
So who created it? Is there a 'canonical' publication of it somewhere?