I thought the letter "г" was supposed to be for the sound "G"?
In the endings of adjectives in the masculine singular genitive (-ого, -его), and in the pronouns его, него, того, самого (also in the singular genitive), the letter г is pronounced as в.
In most tongues which had developed into modern East Slavic languages, the phoneme identified by the letter г was pronounced as a fricative velar (like in modern Greek), not as a plosive velar (like in modern mainstream Russian and English). Even to this date, many Russian speakers, especially in Southern and Western Russia, do pronounce it as a fricative.
In intervocalic position (between two vowels) this consonant was not clearly articulated and had been replaced with a hiatus (short pause). So in the singular genitive endings -ого, -его, the г was silent or close enough to it to make no matter.
Hiatuses do not really work well with Russian prosody (flow and rhythm of speech), so they tend to be replaced with epenthetic sounds (consonants inserted between two vowels or a vowel and an approximant). This is why there's an epenthetic л in the first person singular in verbs like куплю, люблю, an epenthetic д in the prefix над- before the vowels, etc.
The phoneme of choice for adjectives in the singular genitive happened to be в, probably because the labio-dental approximant (the English "w") is easiest to articulate between two rounded vowels and в is the closest Russian phoneme to which it can be perceived as an allophone.
This only works for the adjectives and certain pronouns. In other words, like Того (the country), строго, дорого, много etc., it is pronounced as г.