Sinead O'Connor is known as much for her opinions as music

Uncertainty for several hours Monday over the whereabouts of Irish singer Sinead O'Connor — who was found safe by Chicago-area police after a call saying she hadn't been seen since leaving for a bicycle ride Sunday — was only the latest episode involving the talented but troubled musician.

After scoring an international hit with her rendition of Prince's ballad "Nothing Compares 2 U," O'Connor has been known as much for her fierce and expressive voice as for her blunt criticism of the Catholic Church and other institutions.

O'Connor said she was diagnosed with bipolar disorder more than a decade ago and has spoken publicly of her mental health problems.

The Irish chanteuse warned the younger singer in an open letter in 2013 to avoid being sexually exploited by the music industry after Cyrus released her "Wrecking Ball" video, in which she appears nude and licking a sledgehammer.

Many viewers and church members expressed outrage and weeks later she was booed off the stage at Madison Square Garden during an event honoring Bob Dylan.