It was mistakenly believed that the same was the case with Monroe, his first name supposedly being Eddie. Some sources even reported Monroe being called Eddie in the pilot. However, this is not to be found in subsequent airings of the pilot. Whether it was edited out or 'retconned' by the producers remains unknown. The fact that Monroe is his first name is further supported by Monroe's parents calling him "Monroe", which they theoretically wouldn't do if they shared it as a last name.
Silas Weir Mitchell has gone on the record to state that Monroe's name is "just Monroe", adding that the name Eddie mistakenly got published.