First Z80 was made in July 1976. It was one of the first 8-bit processors.
Its original purpose was to beat out the 8080 made by Intel. It was cool because it
Was made by some ex-Intel Engineers, it had all the 8080 instructions and more.
Other advancements were the extra registers and the RAM refresh signal, which meant lower system cost.

There are tons of variants, upgrades and peripheral chips of the Z80, but these are the specs of the original:

Pin Count: 40
Package: DIP

On-Chip Features-
Emu Mode: Yes
WDT: Yes
Timers: No
Speed (MHz): 6

On-Chip Special Features-
Dynamic Memory
Refresh Counter
Operating Voltage: 5.0V
Ext. Temp: No

Some other Zilog chips of interest are:
Z-180, Z-181 & Z-182, Z-800, Z-280 & Z-380