This is Part 4 of a series to convert Moldvay Basic classes to Chimera. You can find previous instalments via the Race as Class tag, and if you haven’t already read them, it may be helpful to check out the ground rules for conversion. This week’s entry: The B/X thief.
Moldvay describes thieves as “humans who are trained in the arts of stealing and sneaking.” (B10) They can wear leather armour and use any weapon, and they have a bevy of clandestine abilities: Open Locks, Find/Remove Traps, Pick Pockets, Move Silently, Climb Sheer Surfaces, Hide in Shadows, and Hear Noise. Thieves get d4 hit dice and have a back-stab trick that gives a +4 to hit and x2 damage when striking a foe unnoticed (emphasis Moldvay, B10). At higher levels, they can even read magic-user scrolls.
As much as I criticised the magic-user last week, I’ll praise the thief. I know there’s a certain amount of dislike for the class, as it represents a departure from the niche roles filled by the OD&D Cleric, Fighting Man, and Magic-user. I’ll even admit not being a fan of percentage-based thief abilities (except for Hear Noise). 
But the Moldvay thief is a versatile guy (or gal, noted at right) and gets to do all sorts of useful things in the dungeon with his sneaky, stealing skills. If you’ve played any flavour of D&D, you know the drill: Find a chest? have the thief check for traps, then pick the lock. Hit a wall? have the thief climb it. See a guard in the distance? have the thief sneak up and stab him in the cerebellum.
The only hitch is that thieves have to be careful in a fight. While they fight like clerics, they have hit points like a magic-user. And, since thieves can wear only leather armour, they don't last long in melee. If the thief is feeling lucky or has brass balls, he can try sneaking up on foes for back-stabbery. Otherwise, best to hang back and lob a few arrows at choice targets (or, more likely, start checking out the loot while the rest of the party is still fighting...cheeky bastards).
Thieves are humans best described as jacks-of-all-trades. They know a little about everything, but don’t dominate in any of the “traditional” disciplines of combat, spell-casting, or worship. As a result, they tend toward the less savoury and more clandestine aspects of adventuring, which makes them ideal companions in dangerous dungeons full of traps, tricks, locks, and watchful foes. Provided, of course, that they can be trusted.
Swashbuckler: Improve Athletics rolls with acrobatics by level
This is an expanded version of the Burglar Sperk of the same name (CB/7). Backstab combines the act of sneaking up on a victim with a weapon strike. To use it, the thief must be within 1" per level creeping distance of the victim (CB/19) and make a Sneak roll against the foe’s Surprise TN; check results below:
Critical Failure: You draw attention to yourself before you can strike, granting your foe an immediate full action to respond (which may include an attack in self-defence)
Normal Failure: Foe shifts position at critical moment and foils your attempt, though you remain undetected and may make another attempt next round at a penalty of 0-3 (1d4-1)
Normal Success: Attack hits; roll 1 damage die
Critical Success: Attack hits; roll 2 damage dice
That wraps up the human classes—next week, I start with the demi-human freaks.
One thing: As I made this conversion, the class started to seem more “skill-based” than not, which is either proof of the thief’s versatility or an indication that I haven’t done a very good job. So I leave it to you—any comments or criticisms?
I left out Wield, which is what I recommend you use to emulate the read scrolls ability found in B/X (but since the thief doesn’t have any Sperks to access power schools, there’s no actual spell-casting ability). I also left out Fight or Shoot, so if the thief wants to mix it up with any chance of success, he has to buy these as non-class Abilities during char-gen.
Moldvay, Tom, ed. Dungeons & Dragons Basic Rulebook. Lake Geneva: TSR Hobbies, Inc. 1981.
Smale, Erin. Chimera Basic. Atlantic Highlands: The Welsh Piper. 2011.