Qoppa
Qoppa or Koppa (uppercase Ϙ, lowercase ϙ) is a letter that was used in early forms of the Greek alphabet, derived from Phoenician qoph. In Phoenician, qoph was pronounced as a uvular stop (IPA: /q/); in Greek, which lacked such a sound, it was instead used for /k/ before back vowels (Ο and Υ). As the sound /k/ then had two redundant spellings, qoppa was eventually replaced by kappa (Κ). Qoppa remained in use as a letter in some Doric regions into the 5th century BC.
Like all Greek letters, qoppa was also used as a numeral, and had the value of 90. It has continued to be used in this function into modern times, though its shape has changed over time from a Q-like one to a Z-like one (Ϟ ϟ).
In Qoppa was used as a symbol for the city of Corinth, which had the early spelling of Ϙόρινθος. Qoppa is also the source of the Latin letter Q and the archaic Cyrillic numeral koppa (Ҁ).