The invention of the regulator as we know it is usually attributed to Jacques Cousteau and Emile Gagnan in 1942. But its origins can be traced back as far as the early part of the 19th century.
As coal gas began to find widespread application in industry and homes, the need arose for governors to regulate flow and minimise wastage. When Samuel Crossley patented one with a diaphragm in 1825, it was only a matter of time before someone tried to apply the idea to diving.
The first to do so was a Frenchman, Jean-Jeremie Pouilliot of Paris. In December 1826 he applied for a patent on a regulator that used a diaphragm to control hydrogen gas flow to an underwater lamp. It was an addition to this patent, dated 24 August 1827, that first described a pneumatic regulator applied to the art of breathing under water.
In the mid-17th century, Bishop John Wilkins had visualised colonies of people spending their entire lives under water. Pouilliot suggested living at a depth of 100m or more inside an underwater house he called lhydrodome, its rooms, offices and double walls acting as storage for compressed air sent down from a boat on the surface.
Workers known as hydrobats would live in its roof, going out to labour in the fields wearing his hydroploma diving gear, and returning as necessary to recharge their air supply.
Noting that the hydrobats needed to be adequately insured, Pouilliot described their gear as a helmet with a large facepiece and leather sleeves attached to a flared cuirass that covered the upper body, as far down as the elbow joints. His idea was that a man could reach inside to blow his nose (clear his ears) as well as being able to store his handkerchief, snuff box, a small bottle of cordial water, a bun, etc.

Breath-taking suggestion
Pouilliot also claimed that, while the cuirass could have been made with a double bottom to store compressed air, I found it more convenient and comfortable to store it in a special container (worn on the back), similar to that carried by tea-sellers.
His pneumatic regulator was mounted at the top, connected by a tube to the inside of the cuirass. Unlike the finely controlled diaphragm regulator designed for the hydrogen lamp, it used a piston with a relatively crude, insensitive action. Water pressure pushed it down, to operate a rotary inlet valve and allow air to flow from a reservoir.
For exhalations he said: The breathing-out hole is the same as we have seen in diving bells.
The gear was designed to be lighter than water, so a diver could pull himself down using a weight on a chain, then bob up again on releasing it.
Pouilliots regulator patent remained valid for some years, but in 1828 he applied for another one. It was for a simple diving dress supplied with air by a pump on the surface: an arrangement that subsequently served divers for more than 100 years.

Pouilliot intended to control pressure in his underwater house by hanging weights under the piston of a valve, similar to that used in his pneumatic regulator, but it seems he had not worked out a control device suitable for use by a diver in open water. This might, however, have been supplied later in Lemaire dAngervilles patent of December 1828, for an appareil pneumatonautique (see below).
An arm, projecting out in front, is described only as similar to a weighing machine. It is hinged to allow free movement of parts.
In the tradition of patent specifications, these parts are not shown on his diagram. However, by sliding the small round weight out or in along the arm, the diver could bring more or less force to bear on something - perhaps to control air-flow from a piston or diaphragm regulator, of the type already patented by Pouilliot.