Conversation so far:
Who said Kenneth, what is the frequency?“
In 1997, a TV critic writing in the New York Daily News solved the mystery, publishing a photo of the alleged assailant, William Tager.
Who is william tager
On October 4, 1986, while walking along Park Avenue to his Manhattan apartment, Dan Rather was attacked from behind by William Tager, demanding to know Kenneth, what is the frequency?“
Why did William Tager attack Dan Rather
Tager claimed he thought television networks were beaming signals into his brain.

Question: Why did he say kenneth, what is the frequency
Self-contained rewrite: Why did William Tager say, Kenneth, what is the frequency?.