Green’s Dictionary of Slang

(US) a large or important person or thing; often in the phr. the big kahuna.

1964		L.J. Carlino Telemachus Clay 44: He’s the big Kahuna around here. Cool, huh? [...] They call him The Prophet.
1977		D. Kracke How to Turn Your Idea Into a Million Dollars 108: To get the inside information on this market, I talked to Lewis Halper who was for many years a buyer and product director for Sunset House, the Big Kahuna.
1987		(con. 1967) E. Spencer Welcome to Vietnam (1989) 177: I am a witness for those big Kahunas, the B-52’s.
1994		J. Wambaugh Finnegan’s Week 213: Tell me, Big Kahuna, how do your friends over there feel about it?
2000		Little Worker newsletter 🌐 what? Oh my, oh my, oh my...It is not Almighty God the one and only? Then, who is the Head Honcho, the Big Kahuna, the Mero Mero?
2001		N. Green Shooting Dr. Jack (2002) 36: The day when the Big Kahuna is supposed to pull the cosmic flush handle.
2023		(con. 1962) J. Ellroy Enchanters 48: Jack the K’s birthday bash [...] Marilyn [Monroe]’s set to sing ‘Happy Birthday’ to the Big Kahuna [i.e. Jack Kennedy] [ibid.] 277: I got five minutes with the Kahuna [i.e. Bobby Kennedy].