Spiro Agnew was the Vice President of the United States under President Richard Nixon. Forced to resign in 1973 for tax evasion, he was replaced by Gerald Ford.
A clock with a Spiro Agnew caricature clock face was used in the bombing of Mr. Burns' lab. Mona Simpson was one of the people who set the bomb.[1]
Spiro Agnew appeared as the subject of several satirical jokes in a Mad magazine special edition read by Bart Simpson and Milhouse at The Android's Dungeon & Baseball Card Shop. After seeing the repeated jokes, Milhouse assumed Agnew worked for the magazine because it criticized him so frequently.[2]
When Homer was young and found a lamp with a mean genie inside, he asked his dad Abe if he could wish to become the world's yo-yo champion. Abe told his son that it wasn't a good idea because he might do a performance for President Nixon and accidentally kill him, which would result in Spiro Agnew becoming President. Homer then started imagining that very thing happening.[5]
Episode – "Mother Simpson" (on clock face)
Comic story – Hurricane Nixon (mentioned)
Book – C. Montgomery Burns' Handbook of World Domination 
Spiro Agnew at Wikipedia
Spiro Agnew at the Infosphere