Domains: The First Grove, arboreal memory, the elven dead.
Era of ascension: Hykravones, the Shattering. Cohort: current. Eluvarin Aelweir is one of the daemons who survived the Shattering by going elsewhere and coming back wearing a different form, in his case the form of a grove he had not previously been. The lineage the Druids preserve is that he was himself a Druid once, ascended in deep antiquity, broken in the Shattering, and reconstituted as the patron whose body is the first grove the elves walked under.
Worshipped by: The Druidic faction as their founding ancestor; the Amverela, Caerene, Nemo, Eloweir, Istori, Rakiten, Ythari, Teflin, Spindral, and Starborn elves as their ancestor-pantheon source; and effectively every elf who keeps the rite of returning the dead to a named tree. (The worships edge is authored downstream on the worshipper, not here.)
He is the First Grove: the actual standing trees that the Walk of Elves passed through two and a half million years ago, on the migration that took the elven peoples across half a continent before any human language existed. The grove still stands in a place the Druids will not name in writing. Pilgrim trails reach within a day's walk and stop; the last day must be walked alone, and most pilgrims who try the last day return after a few hours, having become unsure of the path. Those who arrive are usually elves who have died once already in a sense the patron acknowledges.
His name is the formal double-word ancestral register, the older form that predates everyday single-word usage. The first word is the name he carried as a Druid before his ascension; the second is the name the grove gave him when he came back wearing it. To say the full name aloud is to ask the patron to be present, and elven loremasters reserve the full form for the year-end rites and for the burial of an elder. Everyday speech contracts to Eluvarin, which the patron also answers to but answers more slowly, as if from further off.
He is not the elven counterpart to the Romance dead-pantheon of human practice. The human dead become silent ancestors in shrines; the elven dead become bark and slow growth in named trees, and the trees are still alive, which means the dead are still arguing. A Druidic priest walking a grove does not so much commune with the past as overhear it. The Shattering's "snuck back as new forms" lineage means the patron is himself an example of what the rite makes possible: a Druidic elder did not exactly die in the Shattering and did not exactly survive it. He came back as the grove, and the dead who go into the grove now go to join him on the same terms.