Green’s Dictionary of Slang

(orig. US) the best, the most exciting, the finest; occas. as adv.; also as phr. the most on toast.

1953		‘Curt Cannon’ ‘Now Die In It’ in I Like ’Em Tough (1958) 51: She’s the most.
1965		W. Dick Bunch of Ratbags 192: Yeah, man, I am really digging the most now. I am hip and crazy-cool, I said to myself. [Ibid.] 194: Us cats were really the most on toast.
1975		L. Rosten Dear ‘Herm’ 90: Cool isn’t the word for him. He is the Most!
1983		Eble Campus Sl. Nov.
1993		Tarantino & Avery Pulp Fiction [film script] 8: You’ll dig it the most.
1999		J. Ridley Love Is a Racket 320: That’s the most, Jackson. The ne plus ultra.