Nobody knows the origin of April Fool's day, but apparently it is widely celebrated all around the world.  Earliest mentions go back to medieval times in Europe.  (Source:  Wikipedia).

Here's a synopsis of the Wikipedia article.
Apparently, nobody can trace the actual beginning of the April Fool's tradition.  However, there are some mentions of the holiday going back to the middle ages all over Europe and the Middle East.  One hypothesis suggests that it goes all the way back to when Noah sent the dove on a "fool's mission" to seek dry land.  But, that can't be true, because according to my research Noah entered the ark in April and sent the dove out 150 days later in September.  But there is a reason for that hypothesis.  Apparently the ancient tradition of "April Fool's Day" was to send someone on a fool's errand.

However, it is this author's opinion that since Noah entered the ark (and sealed it up) in April, then April fool's day acknowledges all the fools that laughed at Noah for building the ark.

Tarot:  "The Fool"

The number of the tarot card that features the fool is one.  I think what is meant by that is that the fool thinks that he/she is solely and independently responsible for his/her successes in life.  The fool thinks that he/she can do it alone.  The fool goes it alone, and fails to recognize that he/she is part of a collective, and that he/she is nothing without others (both spiritual and physical).