Drogoth the Dragon Lord is a Dragon villain in Middle-Earth created for the video game Battle for Middle-Earth II. He is a playable villain for the Goblin faction and appears in the Good Campaign as having taken over the Blue Mountain and needing to be killed. The player is tasked with doing this using the Dwarf army made available to them.
Conversely, in the Evil Campaign the armies of Mordor actively curry favor with him to convince him to ally with them against the forces of good.
As stated above, he was made exclusively for the video game, having never appeared in any other interpretation of Tolkein's works. Generally/canonically, Smaug is supposed to be the last of the Dragons.
In an interesting coincidence, his name sounds similar to that of another dangerous Fantasy series dragon: Drogon, from A Song of Ice and Fire/Game of Thrones.