Level 20
Brother Chthonius (twenty experience levels and still only a brother?) may as well be in charge of several dungeons by now. He has enough power to walk in and pretty much remodel most dungeons from the ground up.
Brother Chthonius, male human Clr20: CR 20; Medium Humanoid (Human); HD 20d8; hp 93; Init +4 (Improved Initiative); Spd 20 ft. (armour); AC 33 (+13 armour, +7 shield, +3 deflection), touch 13, flat-footed 33; Base Atk +15; Grp +18; Atk +24 melee (1d8+8, +5 heavy mace) or +16 ranged (1d4+1, +1 sling); Full Atk +24/+19/+14 melee (1d8+8, +5 heavy mace) or +16/+11/+6 ranged (1d4+1, +1 sling); Space/Reach 5 ft./5 ft.; SA Turn undead; SQ Aura, cast divination spells at +1 caster level, good fortune 1/day, spontaneous casting; AL N; SV Fort +16, Ref +12, Will +24; Str 17, Dex 10, Con 10, Int 14, Wis 26, Cha 12.
Languages: Common.
Skills and Feats: Concentration +23, Diplomacy +3, Gather Information +3, Heal +24, Knowledge (arcana, architecture and engineering, dungeoneering, geography, local, nature, nobility and royalty, religion, the planes) +7, Knowledge (history) +3, Search +2 (+4 secret doors), Spellcraft +27, Survival +8 (+10 underground, +10 to avoid hazards, +10 aboveground, +10 on other planes); Combat Casting, Craft Magic Arms and Armour, Craft Wondrous Item, Extra Turning, Improved Initiative, Lightning Reflexes, Scribe Scroll, Weapon Focus (heavy mace).
Cleric Spells Prepared (6/8/8/8/8/7, base DC = 18 + spell level): 0-create water, detect magic, guidance, light, mending, read magic; 1st-cause fear, comprehend languages, detect secret doors*, detect undead, divine favour, hide from undead, sanctuary, shield of faith; 2nd-aid, augury, detect thoughts*, find traps, make whole, owl's wisdom, silence, spiritual weapon; 3rd-create food and water, dispel magic, glyph of warding, meld into stone, protection from energy*, remove curse, stone shape, wind wall; 4th-death ward, divination*, divine power, freedom of movement, giant vermin, greater magic weapon, sending, tongues; 5th-break enchantment*, flame strike, greater command, scrying, spell resistance, summon monster V, wall of stone; 6th-animate objects, blade barrier, forbiddance, heroes' feast, mislead*, word of recall; 7th-ethereal jaunt, greater scrying, regenerate, repulsion, spell turning*, summon monster VII; 8th-antimagic field, discern location*, earthquake, firestorm, summon monster VIII; 9th-etherealness, gate, implosion, miracle*, storm of vengeance.
* Domain spell. Domains: Knowledge, Luck.
Possessions: +5 heavy mace, +1 sling, 20 alchemical silver sling bullets, +5 full plate, +5 heavy wooden shield, ring of protection +3, belt of giant Strength +4, cloak of resistance +3, gloves of Dexterity +2, periapt of Wisdom +6, phylactery of undead turning, robe of useful items, stone of good luck, sustaining spoon, wand of cure serious wounds [25 charges], wand of searing light [6th-level caster, 25 charges], scroll of cure critical wounds [20th-level caster], scroll of miracle [17th-level caster], diamonds (10,000 gp), assorted gems (5,000 gp), silver holy symbol (25 gp), explorer?s outfit, 2 healer?s kits, 2 flasks of holy water, 257.5 gp.
The skills should come as no surprise now: maxed-out Concentration, Spellcraft and Heal, while picking up more Knowledge skills. By now the only Knowledge skill in which he has less than five ranks is Knowledge (history), but that's no great loss: he's not a bard, so he couldn't benefit from a synergy bonus to Bardic Knowledge checks anyway. He has one last feat, and he uses that to offset another problem arising from a low Dexterity score. Improved Initiative allows him to be a bit quicker off the mark.
With hundreds of thousands of gold pieces to spend, and costs cut by some carefully-chosen item creation feats, Brother Chthonius has a healthy selection of magic items. While his armour and weapons might not be the flashiest items out there, the sheer weight of enchantment ensures that he's very well-protected that he hits hard and often. Gloves of Dexterity +2 get rid of that sub-standard Dex score at long, long, long last -- 4,000 gp and worth every copper, I don't mind telling you. Between that, his cloak of resistance and his Lightning Reflexes feat, his saving throws are quite healthy too. I certainly wouldn't want to go three rounds with him.
Be that as it may, I actually find the process of buying equipment rather tedious: it's far too easy to lose track of one's gold and in the end it just degenerates into a load of bean-counting. The real fun in generating this character was in selecting the spells. By level 20, this cleric finally had access to plenty of offensive spells. Implosion is just plain nasty. Moreover, he's picked up a load of planar travel spells that allow him to be placed pretty much anywhere on any campaign world, meaning that he could quite happily stroll into a high-level adventure and make himself useful to one side or another.
Conclusion
It's not often that I come up with neutral characters. On the whole I leave the business of creating heroes to the PCs while I come up with villains and authority figures. Someone like Chthonius could serve a rather odd purpose. Played well, the PCs could be guessing at his motives for months, trying to fathom him out. He's not a villain, but may provide aid to them if doing so doesn't threaten his notions of balance. By that same token he could also provide timely aid and assistance to the PCs.
Ever since the third edition came out, clerics have started to shake off their reputation for being the 'poor cousins' of the game. Their defensive spells serve a pretty vital purpose in the party, and when combined with the strength of purpose and resolve that come with the character class, they can be among the most influential characters in a game. They are, effectively, the hands of their deities, the agents of higher beings. Such higher beings don't have to be the squabbling sister-shagging pseudo-Olympians beloved of fantasy fiction; even abstract concepts such as fate and fortune can have a divine or spiritual dimension, and that's where characters like Brother Chthonius come in. After all, if dragons can have deities, why not dungeons?