One of the things I always felt AD&D was lacking in was good representations of the forces of Good. I mean we have thousands of demons, devils, daemons, demodands, and everything in-between, but we didn't get anything like an angel until the Monster Manual II and then only three types.
Now the in-game reason is clear, these are not meant to be fought because the assumption is all parties tend towards good. There may have been an outside influence as well. Gary may not have wanted to encroach on his own beliefs here and there was always the nod to pressure from the outside.
With the publication of 3rd Edition and additionally Pathfinder this changed a bit. Now Devas, Planetars, and Solars are classified as angels. But that still leaves open all the different types such as thrones, cherubim, malakim, seraphim, and not to mention the Archangels.
So ignoring all that lore and history, I am still making up my own! Here is one that made appearances in my Buffy RPG games and adapted from my earlier WitchCraft RPG games and had root in my AD&D 2nd ed games.
Angel, Lunar
Large Celestial (Angelic)
Frequency: Very Rare
Number Appearing: 1 or 2d6
Alignment: Lawful [Lawful Good]
Movement: 180' (60') [18"]
Fly: 240' (80') [24"]
Armor Class: 0 [19]
Hit Dice: 13d8+52* (124 hp)
Attacks: 2 by weapon type +5 (STR bonus +3, magic bonus +2)
Damage: 1d10+3 x2
Special: Magic required to hit (+2), 80% magic resistance, spell-like abilities
Size: Large
Save: Monster 13
Morale: 12
Treasure Hoard Class: None
XP: 5,150 (OSE), 5,300 (LL)
Lunars are tall angels with pale skin and wings, golden hair bright eyes. They are the most "human" looking of angels since their duty is to guard human realms. They are the angels who live closest to humans compared to other angelic types. They are typically armed with large glowing swords that they use to perform their primary function, the protection of mortals from demonic forces. Where Planetars deal with evil in general, the Lunars focus on demonic forces and chaotic (evil) monsters and mortals.
These servants of good are always of Lawful (Good) alignment. They will most often be encountered alone (75%) or as part of a hunting party (25%) of 2d6 (7) members. If encountered alone they will be scouting for potential demonic threats, a hunting party has discovered such a threat and have been sent by a Lawful (Good) deity or solar to deal with them.
Lunars have the following Spell-like abilities that they can cast as a Lawful Cleric of 10th level (Wisdom 21). At will: Become Astral or Ethereal, Cure Light Wounds, Know Alignment, Light, Protection from Evil, Remove Fear. 3x per day: Bless, Commune, Continual Light, Cure Serious Wounds, Hold Person, Neutralize Poison, Remove Curse. 1x per day: Dispel Evil, Protection from Evil 10' Radius. Additionally, a lunar may "Turn" undead as a cleric of the 13th level. Demons and chaotic (evil) creatures are affected as if they had a Cause Fear spell cast on them by the lunar. Chaotic (evil) humanoids are allowed a saving throw vs. spells at -4 to avoid these effects. Creatures or characters that are immune to normal fear gain a +2 to their rolls to save. Creatures immune to magical fear sill must make a saving throw, but at +4 to their rolls. Lawful (good) creatures are not affected by this aura of fear. The swords of Lunars are considered to be Lawful intelligent swords, +2. They only function in the hands of a lunar (or it is assumed, a solar of Lawful alignment). Lunars prefer not to kill mortals if they can help it, but will do so if the greater good requires it.
These angels also have 80% magic resistance, are immune to the attacks of undead (ghoul paralysis, mummy rot, life level drain) and lycanthropes. They are resistant to fire and add +4 to any saving throw based on cold or death-related attacks. Their eyes reflect paralysis and petrification gaze back on to the monsters using them. If killed their bodies dissolve in a shimmer of silver light and they are reformed in the Silver City in the Heavens.
Lunars do not trouble themselves in the affairs of mortals except where their primary function of destroying demons comes in. A lunar will for example destroy the summoning circles of demonic magic-users and warlocks and destroy their libraries, but will not actually kill the offending mortal. A lunar may be summoned by a lawful cleric if the proper rituals are followed. Though the lunar will not be under any compulsion to appear, it will get their attention. If the need is great (demon incursion into the mortal realms) then such summoning can be foregone and they will respond to an earnest plea.