Cobalt

A little over one hundred years ago, when Cobalt was at the age of 27, he was traveling with some El-Aurian passengers aboard a transport vessel en route to a quiet planet in the Alpha quadrant. Having escaped near assimilation by the Borg, the thing they wanted the most was to have a peaceful life in some backwater place.
Unfortunately, during the voyage, a warp reactor breach threatened the life of all those on board the ship. The captain of the transport issued a distress call which was picked up by a nearby Federation vessel. That starship, a Miranda class called the USS Caroni, responded the call by going at full speed to the location of the crippled transport, but by doing so, they had to cross a Metreon gas nebula which inflicted severe damage to the Caroni.
Having lost a number of their crew, the captain of the Caroni nevertheless reached the El-Aurian transport and started beaming the passengers onboard, however, the warp core finally reached a critical state and the USS Caroni had to start retreating at impulse speed while still trying to beam people out of the transport.
When the core exploded, the Caroni was hit severely by the shockwave which damaged the ship even further, fortunately, they were already at a safe enough distance and were able to survive the disaster. The Caroni was then assisted by two other Federation ships that reached the place at that time. Cobalt was among those El-Aurians rescued by the Caroni, but his family and a lot of his kind were killed by the accident.
After that incident, Cobalt grew amongst crewmen. Traveling from starship to starship, he valued the Federation for the effort it made to save him and his kind. He always wanted to express his gratitude by serving in whatever means he could. So he spent most of that time working in the various starships he visited in the engineering department, doing whatever the Chief Engineering Officer or any other member of the crew required. During that time, he learned the values of the Federation, and his appreciation toward the organization grew even more. He also spent lots of time hearing other people, offering the shoulder for someone crying and even sometimes he ventured to give a little advice.
Cobalt has always been an adept at repairs, passing most of his time doing some job at a console, a Jeffries tube or an access panel. In his idle times, he prefers to do some reading or work in his personal handheld computer, always trying to study a little bit more, or simply reading some good novel.
Recently, Cobalt has had the feeling that he is no longer a position to help the Federation by being a roaming soul between ships, so he decided to join Starfleet as a way to acomplish this goal.