If you want something that can lead a whole faction then perhaps you could try something similar to Oalian from Eberron. He's (it?) a maxed out wise druid of an awakened great-pine (210-foot) tree and (maybe) Treant. He's the kind of leader that can be confrontational with other non-evil faction without being unreasonable or evil himself. Because of the whole nature thing. Also his faction can have a huge variety of lifeforms and allies. He seems to fit all your criteria (I don't think I have to list them one by one). He's alien enough in biology, while still relatable.

A treant or awakened tree

In Eberron, there is a leader of a nature-based faction who is either a treant or an awakened great pine, named Oalian. Taking him (it?) as a working example of how such a creature could lead a faction, it seems a good fit for your criteria: it's not a standard biped, it lives and breathes, highly intelligent and open for social interactions, not a dragon, a singular being that doesn't need others of its kind to run the faction, classic Western fantasy (Tolkien), and—as Oalian demonstrates—is suited to leading a faction.

A treant or sentient tree is alien enough in biology, while still being relatable.