Fundamentalism is a strong reactionary tendency exhibited by significant minorities within the majority of major religions.
Generally, fundamentalists seek to recapture some sort of supposed ideological "purity," often by reasserting the primacy of ancient religious texts. This puts them at loggerheads with both the secular world and with their more moderate co-religionists.
Fundamentalists of various religions have all or some of the following traits:
- Their rhetoric is often apocalyptic - the end of the world is coming.
- The world become decadent and corrupt.
- Their religion in particular has strayed from the true path and needs to go back to its "original" form.
- Fundamentalists envision themselves as part of a grand cosmic struggle.
- They seize on historical moments and reinterpret them in light of this cosmic struggle.
- They demonize their opposition.
- Fundamentalists are selective in what parts of their tradition and heritage they stress.
- They are led by males.
Fortunately such teaching are often not accepted by the majority. This is especially the case as the world repeatedly does not end on schedule. Funda-mentalism puts the fun and the mental back together. 
- Osama Bin Laden
- Ayatollah Khomeni
- Fred Phelps