Part I: Timothy Gowers on equivalence relations

Part II: Martin Gardner on normal subgroups

Part III: Evariste Galois on normal subgroups

"In all the history of science there is no completer example
 of the triumph of crass stupidity over untamable genius…."

— Eric Temple Bell, Men of Mathematics

See also an interesting definition and Weyl on Galois.

Update of 6:29 PM EDT Oct. 30, 2011—

For further details, see Herstein's phrase
"a tribute to the genius of Galois."