This isn’t about judgements of quality: I just wanted to mention what is surely the soloest album of all time, Boulders by Roy Wood, the great man behind The Move, Wizzard and the only Electric Light Orchestra track I like, ‘10538 Overture’.
Obviously writing and singing and producing every track is common enough, and I’m sure there are many other solo albums where the star plays all the instruments too, though I wouldn’t be surprised if no one else has beaten the sheer number of different instruments he plays here – thirty-something, as I recall. What makes this conclusively the soloest album ever is that Roy also painted the album cover. Short of delivering it to the stores, this would take some beating.