In the context of the series, Herman was begun in 1815 at the University of Heidelberg by Dr. Victor Frankenstein. Work on him was finally completed in around 1850 (neither Lily nor Grandpa is quite sure when) along with his twin brother Charlie. Leaving Germany for Great Britain at a young age, Herman was adopted by the Munsters of Munster Hall, a noble family living in the fictitious Shroudshire, England.
At some point Herman moved to Transylvania (a region in Romania), where he met Lily Dracula. In 1865 (technically at the age of 15, but physically older) Herman married Lily, and eventually the couple and Grandpa (Lily's father) moved to America, where Herman joined the U.S. Army, fighting in World War II.