Shifting gears: which singer went the most drastically different direction after going solo?

Shame that video is only on YouTube in potato quality.

Also, this just serves as an excuse to post this Undertones video:

How 'bout Blondi? She went from Call Me! as Blondi to Ghost Riders as Debbi Harry. Spelling is approximately phonetic.

Darius Rucker went country after leaving Hootie and the Blowfish

Sting bolted away from punk rock of The Police to adult easy listening to a hybrid Renaissance style of music.

Police were not punk by the time they were mainstream. In fact I'd argue they were never punk - although they didn't imitate the sound occasionally on their first two albums. All three were either jazz or progressive rock musicians who culturally appropriated reggae.

That said this is a cool idea.

My first nomination is Shirley Strachan from Skyhooks, who went from this

to this

Also hard to go past Peter Gabriel - I had little time for Genesis but PG's first four albums are seminal. And the world fusion guy he ended up becoming beggars belief.
From this

to

My second tier nominees are Lou Gramm (Foreigner), John Waite (The Babys) and Dave Lee Roth (Van Halen) - mostly because the bands they left also dabbled in the new/softer approach they followed - except in Roth's case where he didn't so much change direction as broaden the palette.

Peter Gabriel or Brian Pern?

Darius Rucker went from the adultish mainstream of Hootie & the Blowfish to country.

I would have called The Police white boy reggae. Some of his later stuff has gone back to the deeper roots of song. This song is from music by Henry Purcell (late 17th century) with lyrics by John Dryden, from the same era.