The Aria storage engine used to be called Maria. This page gives the history and background of how and why this name was changed to Aria.
When starting what became the MariaDB project, Monty and the initial developers only planned to work on a next generation MyISAM storage engine replacement. This storage engine would be crash safe and eventually support transactions. Monty named the storage engine, and the project, after his daughter, Maria.
Work began in earnest on the Maria storage engine but the plans quickly expanded and morphed and soon the developers were not just working on a storage engine, but on a complete branch of the MySQL database. Since the project was already called Maria, it made sense to call the whole database server MariaDB.
Renaming Maria (the engine)
So now there was the database, MariaDB, and the storage engine, Maria. To end the confusion this caused, the decision was made to rename the storage engine.
Monty's first suggestion was to name it Lucy, after his dog, but few who heard it liked that idea. So the decision was made that the next best thing was for the community to suggest and vote on names.
This was done by running a contest in 2009 through the end of May 2010. After that the best names were voted on by the community and Monty picked and announced the winner (Aria) at OSCon 2010 in Portland.
The winning entry was submitted by Chris Tooley. He received a Linux-powered System 76 Meerkat NetTop as his prize for suggesting the winning name from Monty Program.