* James Howlett is his real name.
* Logan is his middle name.
It's likely that the use of "Logan" as his primary name became more common because:
* It's a shorter and catchier name.
* It's more associated with his feral nature and ties to his past.
In the early days of Wolverine's comic book appearances, both names were used interchangeably. However, over time, "Logan" has become the more widely recognized name for the character.