Bush's 69% disapproval is the highest ever recorded
For Bush, or for any president? (link didn't work for me)
One of the other news services said "within the past 70 years." I don't recall what caused FDR to be so low other than the recession, but he's often praised as being on of the top 15 presidents. Just goes to show that in-term popularity polls don't mean much when you are able to look at history and judge the long-term results.
No, he's the most unpopular President in the history of the poll.
If it weren't due to the limited poll history, I'd imagine that Roosevelt's court-packing plan and the downturn of 1937-38 was the cause of his low numbers. The Republicans gained 6 Senate seats and 81 House seats in the 1938 elections, so that was definitely FDR's low point.