I should state at the outset that this is NOT a solo build but it is very POTD party friendly.
RPG Background:
A Keeper of the Wheel is someone who is devoted both to the god Berath and the Nature itself as the embodiment of the cycle of the Wheel, meaning he is both a Priest of Berath and a Druid. Despite understanding the artificial nature of the gods and their origins, he sees them as a necessity, not unlike the Leaden Key in maintaining a proper order to Eora and the Beyond. Not malicious but steadfastly both rational and stoic, he does not flinch at the true nature of the gods and seeks to serve both Berath and Nature itself by seeking a balance between life and death, favouring both in equal balance. To this end he willingly returns back to Eora in service to both Berath and the world.
The Build:
The build is simple but effective and is meant to be a strong support/ healer as well as a consistent buffer/debuffer and reliable DOT dealer. With Priest of Berath and Druid (Animist would be best) you have access both to very strong healing as well as a panoply of corrosive attacks, above all, Touch of Rot, which stays decently useful even at higher levels, in addition to Autumn Decay and many others that you automatically get as a Priest of Berath so the ideal role of this Universalist build is that of healer, buffer and reliable DOT dealer and debuffer. In many ways it is a min-max build. Obviously, stats and race are a matter of preference but I personally like Hearth Orlans the most, both for role-playing reasons and the very high perception, which as a spell caster is essential since accuracy is not gained with level but by other means. Background is optional but I run the White That Wends for even more Perception, so starting stats look like this:
Hearth Orlan
Strength 17
Constitution 3
Dexerity 15
Perception 21
Intelligence 18
Resolve 4
Background is up to you. I went with Mystic from an RPG perspective to play a character who seeks to maintain a balance of the cosmos but that is up to you.
Obviously the Keeper of the Wheel is not a front liner and you are best positioned in-between your front line and back line so all your healing/buffs, etc. affect your party appropriately. The Blessings Of Berath can help pad out the low Resolve and Constitution as well as items in the game. Strength is important both for spell damage and healing, hence as high as can be, Constitution is not terribly important because you are not meant to be taking damage. Dexterity is very important because it allows for rapid casting of spells. Perception is king because all your debuffs and damaging spells typically have very low basic accuracy and A) playing a high perception Hearth Orlan and B) using perception enhancing items as well as auras can give you very good accuracy which allows your spells to crit like mack trucks and generally hit in a reliable manner. Intelligence is needed because of AOE and duration, so that is maxed and as you are not going to be hit much Resolve takes a back line to other stats.
Generally speaking any items that buff Intelligence, Might and Perception are best as well as items that pad out the very low resolve because in POE 2, item bonuses stack. There is ONE item that I regard as absolutely essential for this build and that is a staff called The Spine Of Thicket's Green. It is the perfect weapon for this build because in addition to starting off as an exceptional staff with extra reach being a staff (and you are smudged in the middle of your party, allowing for deadly crit whacks in-between casting from behind the front line) it has a fantastic upgrade called Empowering Life Blood, which gives you +2 Power Levels on all Plant based spells (great for you as a druid) and BOTH Rejuvenation spells (your healing spells as a Druid) AND Restoration spells (your healing spells as a Priest), which is nothing to sneeze as, in addition to having some nice defence upgrades against disease/poison, etc. Finally it can be upgraded to legendary to give it full damage potential. This item is a must because it enhances your damaging/debuffing plant spells and your healing spells for both Druid and Priest! Fortunately this staff is VERY easily obtainable from almost the beginning of the game and can be stolen in the Dark Cupboard magic shop and the upgrade materials can be purchased in Nekata for the healing upgrade, which is essential. It also does +20% damage to vessels.
Everything else is up to you. Obviously, if you do not like support characters and are looking for your main protagonist to be a DPS monster, this build is not for you but if you like healing and debuffing as well as the slow creep of efficient DOT, this may very well be your build. Good luck with maintaining the Wheel and have fun!