Conversation so far:
What does kenneth what is the frequency refer to?
Rather was attacked and punched from behind by a man who demanded to know "Kenneth, what is the frequency?" while a second assailant chased and beat him.
when was he attacked?
On October 4, 1986.
What did they do to Dan?
assailant pummeled and kicked.
What did Dan say about the incident?
Who understands these things?
I didn't and I don't now.
I didn't make a lot of it at the time and I don't now.
I wish I knew who.
Did they find the criminals?
Until the crime was resolved years later.
Did the saying Kenneth, what is the frequency become well known?
The phrase "What's the frequency, Kenneth?" became a popular-culture reference over the years.

Question: What other people started using the phrase?
Self-contained rewrite: What other people started using the phrase "Kenneth, what is the frequency" other than Dan Rather?