Christen was born to Poul Madsen and Ane Johana Christensen in Denmark. Christen, his mother, and his younger brother, Neils Peter, emigrated from Denmark together in 1868 by way of the ship Emerald Isle.The ship roster records his birthplace as Hune, Hjorring, Denmark. Niels and Christen's surname is listed as "Christensen" on ship records and mission records. "Christensen" was the maiden name of their mother, Ane. They were born with the surname "Poulsen," as listed on Christen's birth record. After his arrival to the United States, his surname changed to "Morrison" and is recorded as such in census records and on his death certificate.