When was it invented? The euphonium was invented in 1843
Where? Ferdinand Sommer invented it in Weimar, Germany.
By who? The euphonium was invented by Ferdinand Sommer. However, Carl Moritz and Adolph Sax both made similar instruments during the same time.
The euphonium's ancestor is the serpent- a large instrument with holes like a woodwind, but a mouthpiece like a brass instrument.
The baritone horn is different than the euphonium in its size, and shape. The baritone's tubes are wrapped more tightly together, while the euphonium is a little looser. The baritone has a conical bore, while the euphonium has a cylindrical bore. A baritone typically has three valves, while an euphonium can have three or four.