JOHN JOHNSON

I am trying to find information on John Johnson b. Sweden Nov. 13, 1848. He came to USA and was married to Ellen Obermire Oct. 02, 1875 in Iowa. He died Nov. 17, 1917 in Iowa. His parents were listed as Charles & Mary Oake Johnson. Someone suggested that perhaps the names were Americanized. In talking with family members someone mentioned that his name was Johnny Johnanson (I do not know the correct spelling of the last name). If the names were Americanized what would they be in Swedish? Any suggestion or help will be greatly appreciated. Thanks. Martha Johnson Martha Johnson