One of the more intractable problems for an AD&D e1 DM is the addition of a multiclassed character. They cause a variety of problems. First and foremost, it creates a capability challenge for the DM to work against. Having to plan for spells and abilities is hard enough, but when you have a Magic User and a multiclassed F/MU you might forget the party can do something twice.
This problem could be its own post, so I'll rein it and move on to the commercial. I mean the character. Or both.
I am using my own character sheet which you can download from DriveThruRPG for Regulus, the Fighter/Magic-User/Theif. This Regulus is one variation of the same basic character I used for a friend's campaign. I was the only person who didn't know we were in Narnia and died a zillion times. It got so bad that I stopped making up new names.
Let's start at the top. This sheet has more than your typical slots for information. Its missing a phone number and a blood type, but that is ok.
Not bad for a sheet designed by a committee.
Moving over to the next part, we have class and level information which also has enough space for multiclass information:
Next up is the attribute block. At the time we made this sheet, Unearthed Arcana was new and we wanted to use everything in it. Doug, the DM at the time wanted to use Comeliness for the big villain Jadis. It made perfect sense because that is 50% of how she works.
Beyond this one time, it was a mostly ignored stat. It's too complicated and extraordinarily dangerous for Illusions and Bards to have.
On the far left were armor class and hit points.
There isn't too much to comment on here, except for the Armor condition box. We had this concept that your armor could stand up to about 10 fights without repair. If you didn't maintain your armor, it stopped working. It was basically the fighter equivalent of studying. Unearthed Arcana also had field plate which acted like bonus hit points that could be tracked here.
The box for HP was dual-purpose. First, AE had a couple of spells that would act like hit points so tracking was necessary.
Amusingly, what really happened was you'd burn a hole in the first box erasing and rewriting, so the second box extended the amount of time you could use the same character sheet.
Ingenious, right?
The middle of the page was dominated by the weapons chart.
It had the weapons adjustments, but we never used it despite dedicating so much space to it.
While we all loved AE's new character classes and abilities, somehow we forgot to at the Acrobat's abilities to the thieves' ability chart.
Moving to the left again, we had the other Stats and abilities block. If you were non-human, this would be your favorite place. If you were human, you'd take notes here.
See the weaponless combat table?
Never used. Actually, we did use it once in a Shaolin temple setting and all of the characters died from open-handed Monk attacks.
Silly system.
Next up was the spell table. It was functional and handy, but we didn't have enough room for actual spell names.
Honestly, we just wrote spells on index cards and called it a day. Reg only has 5 spells per day, but if you hop back up to the stat block he actually knows 6 per level.
One odd thing that we did was allowed all magic user types to use the clerical bonus spells from Wisdom. It seemed to make sense.
The other trick we used was magic users always knew Read Magic, Write and Detect Magic spells. If you lost your spell book, this knowledge was necessary to make a new one.
On the second page, and we always had a second page because we used pin-feed printers, was the weapon proficiencies. We were also using the weapon specialization rules from AE.
The second block was for non-weapon proficiencies. This was a block insisted on by me. Even way back then, I had an embryonic idea for a set of skills based on professions. What ultimately became my book Zero to Hero: Uncommon Commoners started with this tiny two-inch block.
Three-quarters of the second page was dedicated to encumbrance.
Remember I mentioned that Bards and Multiclass heroes are the banes of a DM's existence? Bards and Multiclass characters have a tendency of dropping into the background because the other players have surpassed them in combat and magic abilities. When things go badly, they tend to pick over dead bodies. A fine inventory sheet can solve that.
(Unless a sneaky person has 2 or 3 bags of holding...)
Now, I've said very little of Regulus himself, but if you look at this sheet, you can see a special level of trickery going on. In the backpack is a bag of holding. Next to the bag of holding, there is a quiver, a water and wineskin, rations, and a scroll case.
With the quiver poking out the top, my character had virtually no reason to open his backpack at any time outside of camp.
One of our DM's named Mark was driven buggy by characters toting around 3 pouches and a backpack plus a ton of junk in each hand. He said you could have a backpack OR a large pouch and two small pouches. So this is why so many slots appear on our sheets.
For the numerically minded, we had a section for tabulation. Note that the items worn by Reg plus the items that were in the bag of holding don't count toward encumbrance.
Personally, I always like the idea of a smallish pack and two hip-sized pouches.
Anyway, I hope you liked the tour around my characters sheet.
Remember, you can always click those links and download it for yourself. It is dated but I find it charming.
In the Dragonlance lore, there are 3 moons named Solinari, Lunitari, and Nuitari. They were aligned with Good, Neutral, and Evil, and they share their names with gods. As each moon waxed and waned, a spellcaster aligned with that god gained or lost magical spells. 
