I never heard of him before now.
On November 29, 2017, the Star Tribune reported that Keillor was terminated from his position at Minnesota Public Radio for "allegations of his inappropriate behavior with an individual who worked with him". MPR has not released details of any specific allegations beyond that, though Keillor alleges the inciting incident for his firing stems from an incident when he touched a woman's bare back while trying to console her. Keillor claims that he apologized for the incident through email, and received a reply of forgivness from the woman. He says the two "continued to be friendly right up until her lawyer called."
In their statement of termination, MPR notes that they will cease distribution of two programs that Keillor hosted, The Writer's Almanac and rebroadcasts of old epsiodes of A Prairie Home Companion. Additionally, they would be re-titling the successor series, A Prairie Home Companion with Chris Thile, and would eliminate business connections to the PrairieHome.org website.
It's hard to come down on one side or the other based on the limited disclosed facts.
But given that Keillor is famous and established for decades, it's likely MPR investigated and found some basis for the allegations that they were willing to sever ties with someone who gave them a large enduring audience.
Similar to FOX News hiring a law firm to investigate O'Reilly, and despite his being Fox's flagship program, found too many women willing to testify, and cut him loose. O'Reilly still denies he is guilty of misconduct, and while still on air said in such cases (not necessarily his) it was easier to settle than to endure prolonged legal battles to fully clear one's name.