Almanzo Wilder’s name was very unusual and it was often shortened to a nickname by friends and family. Almanzo actually had two different nicknames, one Laura called him, and the other that his family called him.
Almanzo growing up was nicknamed Manny by his family, and it was later used by friends as well.
Laura, however, called Almanzo Manly instead. The story is that Laura misunderstood his nickname at first, mishearing it as Manly instead of Manny. But she thought Manny sounded silly to her, so she changed it slightly to Manly, and she referred to him as Manly for the rest of their lives.
The nickname Manly is also used in the Little House on the Prairie television show too.
Almanzo also had a nickname for Laura, referring to her as Bess as he also had a sister named Laura.