In the Epic of Gilgamesh, Gilgamesh is given the title "He Who Saw the Deep" (Gilgamesh). What is the meaning behind that title?
How that word, here translated as "deep", should be translated is a somewhat contentious issue. The word is nagbu, and there appear to be two main translations to consider.
- Totality, all things
- Abyss, or deep
The former seems to be the most common in translations. The latter was chosen here.
While totality may be the most common in the many translations of Gilgamesh, that may not mean it's strictly the correct choice. Generally, where I can find more in depth explanations on the translation of this particular passage, abyss is often the preferred choice. Their reasoning for the preference refers to usage patterns of the term nagbu in the text, contextual arguments, and the observation that it is reasonably likely to be a reference to the depths appearing later in the story, when Gilgamesh meets Utnapishtim:
...the standard version's incipit is "He who saw the deep" (ša nagbu amāru). The Akkadian word nagbu, "deep", is probably to be interpreted here as referring to "unknown mysteries". However, Andrew George believes that it refers to the specific knowledge that Gilgamesh brought back from his meeting with Uta-Napishti (Utnapishtim): he gains knowledge of the realm of Ea, whose cosmic realm is seen as the fountain of wisdom.
The Epic of Gilgamesh in Prose, Jan van der Crabben
Similarly, John Gardner chooses "abyss" is his translation, but argues that the term may have originally been used to intentionally convey multiple meanings:
...nagbu, which we have translated "the abyss" for the many resorances that the term retains. The term nagbu had a range of meanings, from "spring" and "fountain" and "underground water"--all of particularly great important in arid Mesopotamia, where water is life--to meaning found in poetic texts, "totality," the all. Even as the source of water, it is often used as an epithet of the gods, especially the god whose "place" is the abzu ... Ea, "lord of the deep waters." It is difficult to tell exactly whether Gilgamesh, in seeing the nagbu, has seen the source of waters or "everything." Our guess is that the term is used precisely to capture these multiple meanings.
Gilgamesh, John Gardner
And Jorge Silva Castillo discusses usage patterns of the term and context at length, in which he concludes in favor of "abyss", in his article "Nagbu: Totality or Abyss in the First Verse of Gilgamesh":
...all these considerations lead me to prefer the equation of nagbu in the first hemistich of the poem with the Apsû in Tablet XI 273...Thus in my translation of the poem into Spanish I rendered the first verse "Haré que el mundo conozca / a aquél que vio el abismo," i.e., "Let me make known to the world / him who has seen the Abyss."
"Nagbu: Totality or Abyss in the First Verse of Gilgamesh", Jorge Silva Castillo
(Given that this article addresses this question directly, there is more interesting material than I could quote, or even reasonably address. Do give it a read.)
He also notes that French translators Tournay and Shaffer, while they ended up using the "totality" meaning in their translation, noted that the word may have been intended to be a "jeu de mots", or play on words. This is similar to the note by John Gardner above that the word could well have been chosen for it's multiple meanings.
As far as the word choice of this particular translation:
I haven't found any direct explanation from the translator. As stated in the first quote above, though, Andrew George seems to have concluded that this phrase refers primarily to the knowledge gained with Utnapishtim. His choice of the word "Deep" seems to fall on the side of "the abyss", while favoring a term usage which begs multiple interpretations, to maintain the possible uncertainty. The word Deep is used in modern english to refer to profound knowledge/wisdom, or a physical quality of depth, or the sea, etc.
Given the multiple meanings of nagbu, I would guess the use of such a loaded word with so many possible meanings is a deliberate one.
It means that he learned great wisdom from Ea.
This summary states
The story begins as if by a narrator of a later era. Gilgamesh had all knowledge and wisdom, he was "he who saw the Deep" [Deep=nagbu, the cosmic domain of the god of wisdom, Ea], "surpassing all other kings".
Also worth mentioning is that Wikipedia stats
The later "Standard" version dates from the 13th to the 10th centuries BC and bears the incipit Sha naqba īmuru ("He who Saw the Deep", in modern terms: "He who Sees the Unknown").
. . .
The older version begins with the words "Surpassing all other kings", while the standard version has "He who saw the deep" (ša nagba īmuru), "deep" referring to the mysteries of the information brought back by Gilgamesh from his meeting with Uta-Napishti (Utnapishtim) about Ea, the fountain of wisdom.
Other translations, including this one, imply similar things:
He who saw everything in the broad-boned earth, and knew what was to be known
Who had experienced what there was, and had become familiar with all things
He, to whom wisdom clung like cloak, and who dwelt together with Existence in Harmony
He knew the secret of things and laid them bare. And told of those times before the Flood