Green’s Dictionary of Slang

1. a member of a Mexican teen gang.

1970		J. Wambaugh New Centurions 116: ‘Look, we don‘t care [...] if you want to be stupid and get in gang beefs and die like a stupid vato in the stree’.
1981		J. Ellroy Brown’s Requiem 113: He was a courageous vato, but out of his league.
1990		S. Morgan Homeboy 299: The vatos [...] wrapped their cleanest bandanas around Dippity-Doed razorcuts.
1997		G. Sikes 8 Ball Chicks (1998) 207: Hey, vato! Hey, Ese! La Prima lives!
1997		Kid Frost La Raza‘’ 🎵 Vatos, cholos, you call us what you will.
2006		F.X. Toole Pound for Pound 50: The slick talk of the lawless vatos.
2010		Ice Cube ‘Too West Coast’ 🎵 I know vatos, and they get popped most.

2. in Chicano use, a man, irrespective of race.

1977		E. Bunker Animal Factory 11: The Chicano said, ‘A vato can get killed quick. Every day someone gets hit.’.
1986		J. Ellroy Suicide Hill 51: ‘I know two Chicano dudes, brothers, who're looking for work. Smart—one righteous vato, one tagalong’.
1997		Lil’ Rob ‘Jump in the Ride’ 🎵 on Crazy Life [album] I know it’s something that your hating / But us vatos aren’t faking / So give it up before it’s too late / Cuz you’ll get sprayed if you don’t cooperate.
2019		D. Winslow Border [ebook] [T]he prison is 50 percent over its max and a lot of the vatos are in triples, the weakest guy sleeping on the floor.