https://www.merriam-webster.com/dictionary/OG
Note: According to an essay by Steve Champion and Anthony Ross, former members of the Crips street gang in Los Angeles, the initialism O.G. was first used by the Crips in the early 1970's; see Champion and Ross, "The Making of an O.G.: Transcending Gang Mentality," written in 2006 and available on the website indybay.org as of 7/12/21. The release of the album O.G. Original Gangster by the rapper Ice-T (Tracy Lauren Morrow) in 1991 likely contributed to the migration of the word from gang culture to more general use.