Characters
Who in their right mind, Kevin, could possibly deny that the twentieth century was mine, all of it Kevin, all of it mine?
— John Milton ‧ The Devil's Advocate

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker poses a rhetorical question, daring anyone sensible to deny that the twentieth century belonged to them. Repeating that it was all theirs, addressed directly to Kevin, gives the line a swaggering, proprietary boast that leaves no room for disagreement.
Context reviewed