In the early 1980's, Gaston Glock, who had developed several products for use by the Austrian Military, decided to enter a competition for a new pistol. He had never actually developed a firearm before, but studied the problems and came up with a pistol that met or exceeded all requirements for the Austrian Army.
This pistol was his seventeenth patent, and he labeled it the Glock 17. It was in 9mm and had a frame made with a new light weight polymer with embedded metal inserts to assist in wear reduction and accuracy.
It was and is an amazing design and lead to the company motto, "Glock Perfection."
Here are some examples that I presently own.

Every time I have ever shown one to a non-gunny person, and disassembled it and handed them the frame, they are always amazed at the light weight of the frame.
The metal slide assemble has an extremely tough finish called Tenifer coating. It is very tough and resists corrosion well.
Glock pistols are extremely simple. They have fewer parts than many previous designs.
To disassemble a Glock, you start by removing the magazine.

Then you make certain that the pistol is not loaded.

Then you check again.

Then, pointing it in a safe direction, you pull the trigger.

Holding it like this.

You then pull the slide back about ¼ inch and pull down on both of the take-down levers.

This allows the slide to move forward and to be removed from the frame.

Then you compress the spring slightly, and remove it.

That completes the basic disassembly required for cleaning.
It just doesn't get much simpler than that, now does it.

When lubricating it for re-assembly, I prefer to use a small amount of grease on the wear points.
Unlike oil, grease will stay where you put it for long periods of time.

I put a small amount on the front rails points.

And the rear rail points.

And on the trigger wear points.
Re-assembly is done in reverse order.

Glock now makes several models of their pistol in several calibers, following a sequential order of numbering.
Here they are:
17 - 9mm Standard
18 - Full auto capable 9mm
19 - Compact (Reduced slide length) 9mm
20 - 10mm standard
21 - .45 ACP
22 - .40 S&W
23 - Compact .40 S&W
26 - Sub compact 9mm
27 - Sub compact .40
29 - Sub compact 10mm
30 - Sub compact, 45ACP
31 - .357 Sig Standard
32 - .357 Sig Compact
33 - .357 Sig Sub compact
34 - 9mm Extended slide Competition
35 - .40 Extended slide Competition
36 - Slim line .45ACP
37 - .45 GAP (Glock Automatic Pistol) Short cartridge
There are also several other models that are discontinued or not available in the USA. They also have other designations such as "C" for Compensated, "L" for Long Slide, etc. It takes a lot of effort to know all the Glock designations.
My buddy Tman and I have several versions of the pistol, and have owned and sold many more.
Here's a couple we shot today, a G-22 and a G-26.

Glocks are often either loved or hated by hand gunners.
Some folks simply say that they do not like certain features on the pistol, or that the pistols do not fit their hands as well as other models.
I find the angle of the grip to be nearly perfect for me, although some do not like it.

Some have reported that the slide cuts their hand in recoil, but even though I tend to grip a pistol high, this is no problem for me.

About the only criticism I have about Glocks is that they are difficult to hide for concealed carry.
This is because both the large models and compact models have thick slides. Look at the slides on the M-26 and the M-22.
Some later models have a reduced thickness slide, but they are still "thick" IMHO.

The Glock has no external safety, like on a Model 1911 pistol. Instead, Glocks have a "Safe Action Trigger" assembly.
The shooters must depress this trigger safety to be able to completely depress the trigger and fire the pistol. I find it interesting that those that criticize this trigger assembly often have no problem with double action revolvers, which basically operate the same way.
The thing I appreciate the most about Glocks is that they simply "work". I took my Glock 34 to Thunder Ranch for three training courses and ran about 2,000 rounds through it. It never even hiccupped, even once.

I asked a couple of Instructors about their experiences with student's Glocks and they said they had never seen a problem. When we "set up" failures, like "stove pipes" to train in fixing problems, they would kid with me about how we really had to set these up, as Glocks hardly ever actually had a problem.
Other students with 1911's or Sigs, had to learn to "Apply the Safety", or "Drop the Hammer Block Safety" before holstering their pistol. I just removed my finger from the trigger and holstered mine.
It is as simple to operate as a revolver, but holds 18 rounds of ammo.
To be honest, Glocks have one problem which is a part of their design. To facilitate chambering of the next round, the barrels on some models have a slightly "unsupported" chamber.
This allows the next round to feed easily, but it leaves an unsupported area of the cartridge case in the rear of the cartridge.
Look at this barrel out of a Model 26 and a M-22.
I have never had or even seen a Ka-Boom caused by a Glock chamber allowing a cartridge care to fail. But I have seen this phenoneum in another design, an Astra .40 S&W.
In that instance, the case blew out as a result of being in an unsupported chamber.
It blew the magazine out of the pistol and slightly stunned my hand, but did no permanent damage to me or the pistol.
Glock has addressed this concern and suggests that it is most commonly a result of lead bullet reloads, over-pressured reloads, and poor quality reloads. Therefore, they recommend no lead bullets and only factory loaded ammunition.
Conclusion:
I often wonder at the controversy that surrounds Glocks. I love mine and my Model 34 is my Go-To pistol.
They are truly Perfection.
This pistol was his seventeenth patent, and he labeled it the Glock 17. It was in 9mm and had a frame made with a new light weight polymer with embedded metal inserts to assist in wear reduction and accuracy.
It was and is an amazing design and lead to the company motto, "Glock Perfection."
Here are some examples that I presently own.

Every time I have ever shown one to a non-gunny person, and disassembled it and handed them the frame, they are always amazed at the light weight of the frame.
The metal slide assemble has an extremely tough finish called Tenifer coating. It is very tough and resists corrosion well.
Glock pistols are extremely simple. They have fewer parts than many previous designs.
To disassemble a Glock, you start by removing the magazine.

Then you make certain that the pistol is not loaded.

Then you check again.

Then, pointing it in a safe direction, you pull the trigger.

Holding it like this.

You then pull the slide back about ¼ inch and pull down on both of the take-down levers.

This allows the slide to move forward and to be removed from the frame.

Then you compress the spring slightly, and remove it.

That completes the basic disassembly required for cleaning.
It just doesn't get much simpler than that, now does it.

When lubricating it for re-assembly, I prefer to use a small amount of grease on the wear points.
Unlike oil, grease will stay where you put it for long periods of time.

I put a small amount on the front rails points.

And the rear rail points.

And on the trigger wear points.
Re-assembly is done in reverse order.

Glock now makes several models of their pistol in several calibers, following a sequential order of numbering.
Here they are:
17 - 9mm Standard
18 - Full auto capable 9mm
19 - Compact (Reduced slide length) 9mm
20 - 10mm standard
21 - .45 ACP
22 - .40 S&W
23 - Compact .40 S&W
26 - Sub compact 9mm
27 - Sub compact .40
29 - Sub compact 10mm
30 - Sub compact, 45ACP
31 - .357 Sig Standard
32 - .357 Sig Compact
33 - .357 Sig Sub compact
34 - 9mm Extended slide Competition
35 - .40 Extended slide Competition
36 - Slim line .45ACP
37 - .45 GAP (Glock Automatic Pistol) Short cartridge
There are also several other models that are discontinued or not available in the USA. They also have other designations such as "C" for Compensated, "L" for Long Slide, etc. It takes a lot of effort to know all the Glock designations.
My buddy Tman and I have several versions of the pistol, and have owned and sold many more.
Here's a couple we shot today, a G-22 and a G-26.

Glocks are often either loved or hated by hand gunners.
Some folks simply say that they do not like certain features on the pistol, or that the pistols do not fit their hands as well as other models.
I find the angle of the grip to be nearly perfect for me, although some do not like it.

Some have reported that the slide cuts their hand in recoil, but even though I tend to grip a pistol high, this is no problem for me.

About the only criticism I have about Glocks is that they are difficult to hide for concealed carry.
This is because both the large models and compact models have thick slides. Look at the slides on the M-26 and the M-22.
Some later models have a reduced thickness slide, but they are still "thick" IMHO.

The Glock has no external safety, like on a Model 1911 pistol. Instead, Glocks have a "Safe Action Trigger" assembly.
The shooters must depress this trigger safety to be able to completely depress the trigger and fire the pistol. I find it interesting that those that criticize this trigger assembly often have no problem with double action revolvers, which basically operate the same way.
The thing I appreciate the most about Glocks is that they simply "work". I took my Glock 34 to Thunder Ranch for three training courses and ran about 2,000 rounds through it. It never even hiccupped, even once.

I asked a couple of Instructors about their experiences with student's Glocks and they said they had never seen a problem. When we "set up" failures, like "stove pipes" to train in fixing problems, they would kid with me about how we really had to set these up, as Glocks hardly ever actually had a problem.
Other students with 1911's or Sigs, had to learn to "Apply the Safety", or "Drop the Hammer Block Safety" before holstering their pistol. I just removed my finger from the trigger and holstered mine.
It is as simple to operate as a revolver, but holds 18 rounds of ammo.
To be honest, Glocks have one problem which is a part of their design. To facilitate chambering of the next round, the barrels on some models have a slightly "unsupported" chamber.
This allows the next round to feed easily, but it leaves an unsupported area of the cartridge case in the rear of the cartridge.
Look at this barrel out of a Model 26 and a M-22.

I have never had or even seen a Ka-Boom caused by a Glock chamber allowing a cartridge care to fail. But I have seen this phenoneum in another design, an Astra .40 S&W.
In that instance, the case blew out as a result of being in an unsupported chamber.
It blew the magazine out of the pistol and slightly stunned my hand, but did no permanent damage to me or the pistol.
Glock has addressed this concern and suggests that it is most commonly a result of lead bullet reloads, over-pressured reloads, and poor quality reloads. Therefore, they recommend no lead bullets and only factory loaded ammunition.
Conclusion:
I often wonder at the controversy that surrounds Glocks. I love mine and my Model 34 is my Go-To pistol.
They are truly Perfection.