Although gliders go back to the year 800, I assume you are asking about the engine-based glider and that one is credited to the Wilbur and OrvilleWright also known as the Wright Brothers. They devised several different models beginning with the kite model, and from then on built the first engine-based glider in December, 1903, in the morning, near Kitty Hawk, NC. Which is why North Carolina's license plates read "First in Flight"
HOWEVER you might have heard that there is a debate on whether North Carolina should earn that title, because the first STEADY pilot-managed flight by the Wright Brothers was made in 1905 in Ohio, their native state. So whether NC should be the "first" theoretically, or Ohio, that is something for the historians to try and solve, though I am sure someone on Enotes can tell us more about that.
The first manned glider was flown somewhere around 1630-1632. This was more of a hang-glider made of silk and using the air currents to lift the “kite” and man strapped to the “kite” by harness, into the air. The heavier-than-air glider were created and flown by Sir George Cayley in 1949. Later men like Jean Marie LeBris, John J. Montgomery, Otto Lilienthal and August Moore among others worked toward the flight of these gliders. The first sustained flight was achieved by Otto Lilienthal. The Wright Brothers also developed gliders that wild carry three men. In 1911 the Wright brothers were successful in developing a stable glider.
The glider as we know it today, used mostly for recreation, was developed in Germany and the United States in the 1930’s by Rhon-Rossitten Gesellschaft and Paul, Bill, and Ernest Schweizer respectively.
"A glider—also known as a sailplane—differs from a modern airplane only in that it has no power source of its own. Instead, it uses natural air movements such as updrafts and winds for propulsion and have extremely smooth surfaces. "
We first need to be clear about what we mean by glider. Generally accepted concept of a glider is that it is an aeroplane without engine. Thus there are no gliders with engine, and there are no lighter than air gliders. This is is the original concept of gliders, however with later development of concept of "hang-gliding", now we do have gliders that are not exactly like aeroplanes. Having thus clarified the type of gliders we are talking about, we can get down to identifying inventor of glider.
The first successful glider capable of flying a person was made in England by Sir George Cayley. He used this glider to fly his coachmen across a small valley. However this glider had no capability to control the flying height or direction.
The first glider that can be piloted was made in Germany by Otto Lilienthal in 1891. Lilienthal made about 2500 glider flights between 1891 and 1896.
Wright brothers in USA also experimented with gliders before developing powered aeroplanes.