G is the seventh letter

Letter (alphabet)

A letter is a grapheme in an alphabetic system of writing, such as the Greek alphabet and its descendants. Letters compose phonemes and each phoneme represents a phone in the spoken form of the language....

 in the basic modern Latin alphabet

Basic modern Latin alphabet

The International Organization for Standardization basic Latin alphabet consists of the following 26 letters:By the 1960s it became apparent to the computer and telecommunications industries in the First World that a non-proprietary method of encoding characters was needed...

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The letter 'G' was introduced in the Old Latin period as a variant of ⟨c

C

Ĉ or ĉ is a consonant in Esperanto orthography, representing the sound .Esperanto orthography uses a diacritic for all four of its postalveolar consonants, as do the Latin-based Slavic alphabets...

⟩ to distinguish voiced, /ɡ/ from voiceless, /k/. The recorded originator of ⟨g⟩ is freedman Spurius Carvilius Ruga

Spurius Carvilius Ruga

Spurius Carvilius Ruga was the freedman of Spurius Carvilius Maximus Ruga. He is often credited with inventing the Latin letter G. His invention would have been quickly adopted in the Roman Republic, because the letter C was, at the time, confusingly used both for the /k/ and /g/ sounds...

, the first Roman to open a fee-paying school, who taught around 230 BC. At this time ⟨k

K

K is the eleventh letter of the English and basic modern Latin alphabet.-History and usage:In English, the letter K usually represents the voiceless velar plosive; this sound is also transcribed by in the International Phonetic Alphabet and X-SAMPA....

⟩ had fallen out of favor, and ⟨c⟩, which had formerly represented both /ɡ/ and /k/ before open vowels, had come to express /k/ in all environments.

Ruga's positioning of ⟨g⟩ shows that alphabetic order, related to the letters' values as Greek numerals

Greek numerals

Greek numerals are a system of representing numbers using letters of the Greek alphabet. They are also known by the names Ionian numerals, Milesian numerals , Alexandrian numerals, or alphabetic numerals...

, was a concern even in the 3rd century BC.