As you can see in the Anukramani I provided in my answer herehere, the sage who heard most of the hymns in the Fourth Mandala of the Rig Veda was the sage Vamadeva, a descendant of the sage Gautama. Two of the hymns of this Mandala deal mainly with Garuda's theft of the Soma/Amrita (nectar of immortality) from Devaloka. But the beginning of these hymns are considered by the Upanishads to be of profound significance. Here is how Hymn 26 of the Fourth Mandala begins:
So the Aitareya Upanishads is claiming that the speaker is once again Vamadeva, and that he is speaking of his experiences of self-realization from within the womb. And the Rig Veda Anukramani agrees that the person being referred to is Vamadeva in both cases; see the Anukramani for hymns IV.26 and IV.27 in my answer herehere.