While it was certainly not the first overdrive pedal, the Ibanez Tube Screamer definitely has been one of the most successful and influential guitar pedals ever made. The classic three controls -- Drive, Tone and Level -- allow for a wide range of tube-like overdriven sounds. There are two general approaches players tend to take when using a Tube Screamer. One is to use it to generate its own overdrive tones by turning up the Drive knob and then adjusting the output level to taste. This will give even an amp set for clean tones a nice overdriven sound. The second approach was famously used by Stevie Ray Vaughan. He set his TS-808 more as a clean boost than as a "distortion" pedal; the idea being that by pushing the output level, he could drive the input of his tube amps harder, causing them to distort instead of getting the majority of the overdrive from the pedal. This is still a commonly used approach with the TS family pedals, and it works very well with small, lower-powered tube amps that are on the edge of breaking up.
The TS808 was the first Tube Screamer, and it was in production from the late 1970s until about 1982, when the TS-9 took its place. The TS-808 has reissued since then, and is still available with the same circuits, cases, cosmetics and sound as the originals - it's even been made in a hand wired, point to point version -- the TS808HW. The TS808 is generally considered the holy grail of the TS family, and is slightly smother sounding than the models that followed it. Original TS-9 Tube Screamers were made from about 1982 to 1985. The TS-9 was reissued in 1993 and has remained in production continuously since that time. The TS-808 and TS-9 are the two "classic" Tube Screamer pedals, and the most highly sought after models, but there were others. The TS-10 was introduced in 1986, and used PCB mounted power, input and output jacks, which tended to break easier than the case mounted jacks of the earlier Tube Screamers. It was superseded by the TS-5, which used similar PCB mounted construction. Part of the Daphon built "Soundtank" series, these had a vaguely bug shaped black plastic case and a circuit design that more closely matched the original pedals than that of the TS-10 did. Metal cases made a return in 2000 when the TS-7 Tone Lok series pedals were introduced as replacements for the TS-5. Up until late in 2002 when Ibanez switched to a new factory, most Ibanez Tube Screamer pedals (with the exception of the previously mentioned Daphon built TS-5) were actually manufactured for Ibanez by Nisshin Onpa - the makers of Maxon pedals. Maxon continues to make similar TS influenced models today, as do many other companies and boutique pedal builders. In fact, the Tube Screamer remains one of the most highly copied and adapted pedal designs of all time.