Who is Martin Luther?

Here :)

Explanation:

Martin Luther, a 16th-century monk and theologian, was one of the most significant figures in Christian history. His beliefs helped birth the Reformation which would give rise to Protestantism as the third major force within Christendom, alongside Roman Catholicism and Eastern Orthodoxy.

your word would be isle.

isle is an island or peninsula especially a small one.

if you add the letter "a" you get aisle, which is a passage between 2 rows of something like chairs, shelves, or something else.