How many people or things can you think of that are indisputably first in their category? For example, A is the first letter of the English alphabet.

(Possible) Answers:

A - first letter of the English alphabet
Alpha - first letter of the Greek alphabet
1 - first counting number
January - first month of the year
Sunday - first day of the week
Hydrogen - first element on the Periodic Table
Kindergarten - first class of public school
George Washington - first president of the United States
Mercury - first planet in order from the sun 
John Glenn - first American to orbit the Earth
Neil Armstrong - first man on the moon 
Mary Lou Retton - first female athlete on a Wheaties box
Jeannette Rankin - first woman elected to U.S. Congress 
Elizabeth Blackwell - first woman medical doctor in the U.S.