Artscroll translates it as "the supreme G-d". Koren offers us, "G-d most high". The phrase they are struggling to accurately translate is "Keil Elyon" which is found at the outset of our Shemone Esrei which describes Hashem as, "the great, the mighty and the awesome, Keil Elyon".
At first glance, "Elyon" seems to describe something relative to others. To be sure, the Bais Hamedrash Elyon of Monsey was happy to recognize that there are other kollelim as long as "Elyon" accorded the top spot to the Monsey Bais Hamedrash. Certainly there were decades when it trained some of our elite, as it was headed by Harav Reuven Grozovski zt"l and Harav Gedalya Schorr zt"l. They would certainly say that their students were "supreme" to those of competing kollellim. According to Koren they are "most high." Are there others who were just "high" and still others who were "less high"? Similarly, the students at the Kollel Elyon at RIETS would certainly recognize that they are elyon to the other kollelim in the yeshiva, where they themselves studied en route to becoming part of this cadre of very fine budding scholars.
But Artscroll, Koren, you, and I cannot countenance a description of the Ribono Shel Olam which seemingly compares Him to others like Him. As true as the superlative is, using a comparison which seems to imply there are others should invalidate the phrase as an apt reference to Hashem.
Indeed, the phrase was not homegrown. We first learn of it in our parsha (14:18- 20) from Malki Tzedek who was king of Shalem and "priest to Keil Elyon", as he graciously welcomes Avrohom. Undoubtedly the king was overwhelmed by the stunning military victory of Avraham's seemingly paltry force over the ruling empire of the time. Avrohom, the aggressive and confrontational monotheist who was vindicated to all at this miraculous moment, does not correct his host as he thanks Keil Elyon for delivering Avrohom and confers the blessings of Keil Elyon on him. Moreover, Avrohom (14:22) invokes Keil Elyon in the oath that he subsequently takes to distance himself from receiving any material benefit from the spoils of the recently won war. It is clear that Avrohom knew that "Keil Elyon" was correct description to use.
The same discomfort apparent from the wordiness of Artscroll and Koren most likely motivated the Vilna Gaon (quoted in the Siach Yitzchak) to translate the phrase as, "the one who is above our understanding."
Why did Chazal include this accolade in the introductory blessing of Avos? Why conjure up in our minds the Avrohom-Malki Tzedek repartee every time we turn to Hashem in prayer?
Perhaps an insight that I found in the collected writings of Harav Yisachar Teichtal (the author of the Eim Habonim Semeicho) sheds light on this and adds meaning to our daily davening. He pointed to the medrashic opinion that understood that Avrohom's oath distancing himself from enjoying the spoils of war was in fact a "shira", a great song to Hashem. Rav Teichtal explains that by refusing to benefit from the miraculous battle, Avrohom was expressing that simply carrying out Hashem's will and being part of His miracle was reward enough. In fact, to accept material profit would trivialize the moment.
Thus the first time our ancestor uttered "Keil Elyon" he had just returned from a life-threatening mission in which he risked everything in order to save his nephew, and yet when he came back whole he did not feel any more entitled as a result. Instead he was grateful to be privileged to be called upon by Hashem and he recognized that the One who defies understanding in difficult times and moments of challenge also defies understanding when He showers opportunity and privilege on us as well. Simply put, while so many ask, "Why did I have to suffer? Why was I in pain?", Avrohom was asking "Why was I privileged? Why did I merit?"
How different our davening would be if when referring to Hashem as Keil Elyon we too would take stock and feel profoundly grateful for the opportunity to daven, and perhaps even blessed with more than to which we are entitled.