He was in power from his election in 1932 until his death in office in 1945, after being elected a record 4 times. (It was a record because after he died they added the 22nd amendment to the constitution that said you could only serve 2 terms)
He developed a paralytic illness just before he turned 40, originally diagnosed as Polio but what many people nowadays think was Guillain-Barre syndrome (with all the natural limits of retroactively diagnosing people.)
He didn't use his wheelchair much in public, preferring to obscure that to the point where some foreign leaders didn't even know he was disabled.
He set up the Warm Springs Institute, a polio rehab centre, which is one of my personal favourite places, pretty much exclusively because they kept really extensive historical records.
He also features in their "Polio Wall of Fame" which tickled me, so I had to somehow shoehorn that in and tell you all.