Who is the seer of the Isha Upanishad?

Question

As I discuss in this answer, each of the four Vedas consists of four portions: Samhitas, the core part of the Vedas which consist of hymns heard from the gods; Brahmanas, commentaries on the Samhitas which provide instructions on the proper conducting of important rituals; Aranyakas, which provide instructions for rituals meant for forest-dwellers and hermits; and Upanishads, which consist of conversations between teachers and students which clarify the philosophical message of the Vedas. But when someone says, e.g. "I read the Rig Veda" without qualification, they usually mean the Samhita of the Rig Veda, because the Samhitas are the core part of the Veda which are of divine origin; the verses of the Samhitas come from sages known as Dhrishtas (literally "seers") who heard them directly from the gods, and then these verses were compiled by a sage named Krishna Dwaipayana Veda Vyasa (or Vyasa for short). The Brahmanas, Aranyakas, and Upanishads are works that were mostly later added on as supplements and commentaries for Vyasa's Samhitas.

But there is one Upanishad that has a very different origin - the Isha Upanishad, AKA the Ishavasya Upanishad. It isn't some supplement or commentary, it's actually part of one of the Samhitas themselves; it's the 40th Adhyaya of the Vajasaneyi Samhita, which is the Samhita of the Shukla (white) version of the Yajur Veda. (Here is another translation of the Upanishad.) This means that the Isha Upanishad isn't just someone's philosophical teachings like the other Upanishads, rather it's a hymn heard directly from the gods.

So my question is, who is the seer of the Isha Upanishad, i.e. the sage who heard it from the gods? If I had to guess, I would guess that it's the sage Yajnavkya, who's associated with the Vajasaneyi Samhita in general, but I'm not sure. Also, since the verses of the Vedas are usually addressed to some god or the other, who is the Isha Upanishad addressed to? The last few verses are addressed to gods like Pushana and Agni, but who are the earlier verses addressed to?

This is the sort of information that can be found in the Anukramanis, a set of systematic indices for the Vedas which, among other things, documents the sage who heard each verse from the gods, and the deity that each verse is addressed to. In this answer, I compiled the sage and deity information for most of the hymns from the Anukramani of the Rig Veda Samhita, but the Yajur Veda Anukramanis don't seem to be so easily accessible. Apparently there is one Anukramani for the Vajasaneyi Samhita, as described in this book:

The third Anukramani, that of the Madhyandina-Shakha of the Vajasaneyaka, is ascribed to Katyayana, who is mentioned also as the author of an Anuvakanukramani. It gives the names of the poets, the deities, and the meters, for all the verses of the Samhita, including the Khila (Adhyaya 26-35), and the Sukriya portions (Adhyaya 36-40).

That seems like exactly the work I want, because it has information for Adhyaya 40, which is the Isha Upanishad. So does anyone know whether Katyayana's Anukramani of the Madhyandina Shakha is available online, or if it's even been published in book form, whether in Sanskrit or in English?

Note: I posted a separate question to try to find the Anukramani information for the Vajasaneyi Samhita.

Answer 1

There are three levels of Rishis in Vajasaneyi Samhita.

The Sarvanukrama Sukta of Vajasaneyi Samhita states the Rishi for whole Vajasaneyi Samhita is Rishi Vivasvan. He is the first level of Rishi.

इषेत्वादि खं ब्रह्मान्त विवस्वान् ।।
It was taught by Vivasvan (hence he is the Rishi).

Thus the Rishi for whole Vajasaneyi Samhita is Rishi Vivasvan.

Then comes second level of Rishi. Second level of Rishi are those who became Rishi due to being prescribed by Brahmanas and they are Rishis as per divisions made by Brahmanas. It states:

ततः प्रतिकर्म - विभागेन ब्राह्मणानुसारेण ऋषयो वेदितव्या ।।
Thus the ritualistic division as per the Brahmana and they are Rishi.

It also states these Rishis are "DarshaPurnamasa Vishesha" and they are of Deva level. It also gives two exceptions who are not Devas but still can be Rishi of this level. They are Yajnavalkya and Dadhyang Atharvan.

Then again there is Third level of Rishi who became entitled with the position 'Rishi' due to mastery in respective Vedic mantras. They are called Vaiyektika Stara Sambaddha Rishi.

Now coming for:

Isha Upanishad:

Isha Upanishad is the 40th chapter of Vajasaneyi Samhita.

Rishi:

Rishi in 1st level = Rishi Vivasvan

Rishi in 2nd level = Rishi Dadhyang Atharvan

Rishi in 3rd level:

1st verse to 14th verse of Vajasenayei Samhita = Rishi Dadhyang Atharvan

15th verse and 17th verse of Vajasaneyi Samhita = Rishi Dadhyang Atharvan, Brahma

16th verse of Vajasaneyi Samhita = Rishi Agastya.

Devata:

The Devata is Atma for 1st to 14th verse and 17th verse. The 17th verse is:

हिरण्मयेन पात्रेण सत्यस्यापिहितं मुखम्  ।
तत्त्वं पूषन्नपावृणु सत्यधर्माय दृष्टये॥
17 The Real's face is hidden by a vessel formed of golden light. The Spirit yonder in the Sun, the Spirit dwelling there am I. OM! Heaven! Brahma.

The Devata is both Atma and Paramatma for verse 15:

वायुरनिलममृत ।  मथेदं भस्मान्त शरीरम्  ।
 ॐ क्रतो स्मर कृत स्मर । ॐ क्रतो स्मर कृत स्मर ॥
15 My breath reach everlasting Air! In ashes let my body end. OM! Mind, remember thou; remember thou my sphere; remember thou my deeds.

The Devata is Agni for the 16th verse of Vajasaneyi Samhita:

 अग्ने नय सुपथा राये अस्मान् विश्वानि देव वयुनानि विद्वान्  । युयोध्यस्मज्जुहुराणमेनो भूयिष्ठां ते नमौक्तिं विधेम  ॥
16 By goodly path lead us to riches, Agni, thou God who knowest all our works and wisdom. Remove the sin that makes us stray and wander: most ample adoration will we bring thee.

One can read the above information of Rishi, Devata, Chhanda with the Samhita also (in Hindi and Sanskrit) from this book named Yajurveda Samhita.

Answer 2

So my question is, who is the seer of the Isha Upanishad, i.e. the sage who heard it from the gods? If I had to guess, I would guess that it's the sage Yajnavkya, who's associated with the Vajasaneyi Samhita in general, but I'm not sure. Also, since the verses of the Vedas are usually addressed to some god or the other, who is the Isha Upanishad addressed to?

According to the commentary of Sri Raghavendra Swami here, the Rishi is Svayambhuva Manu and the Devata is Hari with the name 'Yajna.'

Line number three of the document reads (after my transliteration to English)

asyA upaniSadaH svAyambhuvo manu RSiH yajnanAmA harirdevatA

The last few verses are addressed to gods like Pushana and Agni, but who are the earlier verses addressed to?

I am not sure what all traditions consider like what you said above but at least according to Srila Prabhupada (Madhva Gaudiya Sampradaya) these prayers are to the Supreme Lord Himself as one can see here in his commentary to Isopanisad.