What pen is compatible with a 1st generation iPad?

No Apple Pencil is compatible with original “first generation” iPad.

Apple Pencil (2nd generation)

You can use Apple Pencil (2nd generation) with these iPad models: 

• iPad Pro 12.9-inch (3rd generation) and later
• iPad Pro 11-inch (1st generation) and later

Apple Pencil (1st generation)

You can use Apple Pencil (1st generation) with these iPad models:

• iPad Pro 12.9-inch (1st or 2nd generation)
• iPad Pro 10.5-inch
• iPad Pro 9.7-inch
• iPad Air (3rd generation)
• iPad (7th generation)
• iPad (6th generation)
• iPad mini (5th generation)

Not sure which iPad you have? Identify your iPad model.

The link at the bottom of my previous reply will help you to identify any iPad model.

However, as already stated, Apple Pencil is not compatible with your first generation iPad.

As for other third-party stylus, these are entirely reliant upon explicit support being provided by Apps. Given the age of your iPad1, now obsolete, you’re not going to be able to find compatible Apps for your iPad.

The final IOS release for iPad1, in September 2012, was iOS 5.1.1. It cannot be updated to any later major version of iOS as it lacks the minimum hardware requirements needed to run more recent versions. Most App Developers have dropped support for older devices and iOS versions preceding iOS11/12/13 - and have withdrawn older versions of their Apps from the Apple App Store; nothing will be available for iOS 5.1.1.

If Apps that you need to use now have higher minimum iOS-version requirements, your only option is to replace your iPad with newer model. Of available models, even the entry-level model is lightyears ahead in capability and performance of you existing iPad - and supports Apple Pencil, iPadOS 13.x and the majority of App titles.

Are you talking about a 2010, 10-year old iPad 1st generation ?

Absolutely none!

None, at all!

No iPad made before late Fall 2015 is compatible with ANY Apple Pencil.

Older iPads are missing a crucial internal hardware screen layer needed for an Apple Pencil to interact with these older iPad screens.

There is no Apple Pencil-like, smart Bluetooth stylus that I can, honestly, recommend, currently for older iPad models.

The one I usually recommend, the Adonit Pixel stylus, has been out of stock, everywhere, for months, due to the worldwide pandemic, as there is no way to predict when this stylus will be available, again, if at all!

You have other stylus options like found everywhere, commonplace, capacitive stylii to use with your older iPad Air.

The better, more accurate versions of these are capacitive stylii with a clear disc tip for more accurate drawing.

Another type of commonplace capacitive stylii is the fine tip/ballpoint-like tipped, battery operated, so-called “active” stylus that uses a tiny battery to send small electrical signals to a fine point tipped stylus that mimics an actual finger touch.

All of these types of stylii suffer from varying degrees of line wobble when drawing angular lines. Some are worse than others.

The better of both the disc tipped stylii and the battery operated “active’ stylii are made by Adonit stylii.

https://www.adonit.net/pro4/

https://www.adonit.net/dash/

Like all commonplace, capacitive stylii, none of these stylii have screen pressure sensing OR palm rejection.

So, you will not be able to draw thin to thick or light to dark lines with these types of stylii.

The exception to this limitation is if the sketching/drawing/painting/writing app has a programmed/coded-in feature to drawing thin to thick/light to dark lines using velocity or how fast you draw a mark across the iPad's screen using a finger pr commplace, capacitive stylus.

Some sketching/drawing/paining/writing apps have this velocity line varying marking feature.

So, you can write or draw on the iPad's screen with the palm or side of your hand down on the iPad’s screen and NOT make stray marks on the iPad's screen, with various sketching/drawing/paintng/writing apps, there are inexpensive special non-body electrical conducting, lycra- material based drawing/writing gloves for touch screen devices that allow you to lay the palm/side of your hand on capacitive touch screen tablet that isolates your actual hand from the tablet's screen so it will not send any electrical signals to the tablet’s screen and not make false or accidental touches while using an iPad or other capacitive touch screen device while writing or drawing.

Something like this found on Amazon.

https://www.amazon.com/Professional-Anti-fouling-Drawing-Tablet-Graphic-Right-Ha nd-Left-Hand/dp/B017R8M2JY/ref=sr_1https://www.amazon.com/Professional-Anti-fouling-Drawing-Tablet-Graphic-Right-Ha

Many more makers of these types of gloves found on Amazon and in different hand sizes and colors, as well!

Best of Luck to You!

You will have a further issue though....having drawing apps that run on iOS5.1.1 that also work with a bluetooth stylus.

If you really want to draw and do artwork/graphics on your ipad you may have a better experience updating the ipad to a newer model. This will make compatibility with drawing apps and bluetooth styli easier.

Skydiver119 is correct.

If you do not already have some older drawing/sketching/painting and handwriting/notes apps on that iPad, already, you will no longer find any such apps for that iPad and that old an iOS version.

As Lotus said, no pencils will work with your device, it's simply to old