Who was the first person inducted in the Rock 'n' Roll Hall of Fame?

I'm afraid I can't find a definitive answer at the official Rock and Roll Hall of Fame website. CNN says it was Chuck Berry, although I did find another source that says it was Elvis.

I'm inclined to think it was probably Elvis, as a posthumous first induction would have seemed more fitting than choosing between living performers, presumably in attendance, however, from a researcher's point of view, I have to choose what I consider to be a more credible source, and in this case, CNN won out over Bill Miller, whoever he is.

It was actually Robert Johnson, "The most important blues singer that ever lived." - E. Clapton

There were 15 inductees at the first ceremony. Chuck Berry was the first.

1986 INDUCTION CEREMONY

After more than a year of planning, the debut of the Rock and Roll Hall of Fame Induction Ceremonies took place in the Waldorf-Astoria's Grand Ballroom in New York City on January 23, 1986. Early on, plans were in the works to construct a museum, whose location was under discussion, with possibilities including Cleveland, Memphis, Philadelphia, Chicago, and New Orleans. Represented were the major strains of music that emerged to form rock & roll: rockabilly, R&B, blues, country and gospel. Those doing the inducting came from both behind the scenes, such as influential DJs Norm N. Nite and Scott Muni (for Alan Freed), and the spotlight, including Billy Joel (for Fats Domino) and Steve Winwood (for James Brown).

Legendary promoter Bill Graham orchestrated the off-the-cuff performances, shouting direction and coercing reluctant artists onstage. Fogerty belted out "Proud Mary," the first time he'd performed the Creedence Clearwater Revival song in public since 1972. Another music standard-bearer providing backup was Paul Shaffer with the World's Most Dangerous Band (from Late Night with David Letterman), which included saxophonist David Sanborn, guitarist Sid McGinnis, bassist Will Lee, and drummer Steve Jordan.

Inductions got underway with a festive Keith Richards ripping off his tux jacket and exposing a flashy leopard-print jacket underneath, appropriate for inducting Chuck Berry: "It's very difficult for me to talk about Chuck Berry 'cause I've lifted every lick he ever played -- this is the gentleman who started it all!"

https://www.rockhall.com/inductees/classes