Coming into D&D in the early 80's with the red box set and then quickly onto AD&D I had no idea that there were some who'd been playing the game since its release in 1974 that considered the Thief class to have broken the game.
While I very much enjoy the original LBB (little brown books) that are so bare boned there was only 3 classes: Fighting-Man, Magic User, and Cleric. I find that Greyhawk really completes the original set.
There is general agreement that Greyhawk which introduced variable damage and hit dice, ability score bonuses and penalties, and a variety of other things really fixed the game. Yet the thief seems to have stolen some of the primary things players were doing on adventures that hadn't quite been systemized yet: sneaking around and stealing stuff.
The thief is a staple now of just about any fantasy roleplaying game. Enjoying a special niche all their own separate from the fighting ability and spellcasting ability of other classes. There is however a problem with the thief that I haven't seen much written about. That is how bad they are at their character abilities.
A 1st level thief can pick pockets with a 20% chance of success. You know from actually playing one that is terrible, there is an 80% chance of getting caught! All those other things are so bad there is hardly a point in even trying until higher levels, 15% to open locks? 10% to remove traps? Oops! Triggered again, the party is dead. Yikes. What if we got rid of all that stuff and they were really good at one thing first. What if pick pockets started at a 60% chance of success? Now we're talking. Then it could improve at a slower rate and eventually become very proficient.
What if they slowly acquired the other abilities as they leveled up? Then they would be in synch with the other classes. With this idea in mind here is a reimagined Greyhawk-style thief class. A note on terminology, a few things are changed to be more generalized; for example the general term pilfering instead of the specific term pick pockets. Or climb instead of climb walls.
Each level opens a new Thief Class Ability. Success is not determined by a percentage, an idea I find doesn't fit the rest of the mechanics of the game, but by an ability check. The GM could adjust the difficulty of the task up or down. If the victim is attentive and other leery viewers in the area a pilfering attempt may be more difficult. If the victim is asleep success may almost be assured with only a roll of 1 waking the target up and getting caught. The level of the character and dexterity adjustment may be added to the roll of a d20 for success.
Prime Attribute: Dexterity, 13+ (+5% XP)
Hit Dice: 1d4
Armor/Shield Permitted: Any non metal. No shield.
Weapons Permitted: Any one-handed.
Pilfer: at 1st level the thief can filch small objects, pick pockets, and palm small items without being noticed.
Open Locks: at 2nd level the thief can open any lock given enough time and with the right tools.
Hear Noise: at 3rd level the thief is sensitive to sounds others may not notice, and identify what they are or what someone who is speaking in a language they understand is saying.
Climb: at 4th level the thief can climb sheer surfaces including walls and cliffs.
Backstab: at 5th level the thief can deal double damage when striking an opponent from behind. At 7th level damage is x3. At 9th level damage is x4.
Disarm Traps: at 6th level the thief can render a trap inoperable given enough time and the right tools.
Move Silently: at 7th level the thief can move at half speed without making a detectable sound.
Hide in Shadows: at 8th level the thief can become near invisible when lurking in shadows, they may slowly crawl at a rate of 1”.
Read Languages: at 9th level the thief can read any language they may have reasonably come in contact with, including magic. This ability allows them to use magic-user scrolls, though with a high degree of error. Reading languages excludes lost, ancient, extremely foreign, or dead languages that would require special knowledge to know.
Thieves Guild: at 10th level the thief becomes the master of a local thieves guild in a fortified hideout, usually in a seedier part of town, that will attract 2-12 apprentices. This hideout is difficult to find and infiltrate. They will also have political influence with corrupt officials and powerful criminal elements.