Rebecca Rae (Tremain) Sinclair was born in Phoenix, Arizona, the only child of Marie and Arturo Tremain. Her father was an officer on Phoenix's peach keeping force and her mother was a hydroponic farmer.

Rebecca showed intellectual promise at an early age and at age ten was sent to Denver, Colorado to study at the Allensworth Institute. While at the Institute, Rebecca became interested in space exploration. She accessed everything she could find on the subject and became fascinated with Starfleet. As soon as she was old enough, she applied to Starfleet Academy and was delighted when her first application was accepted.

Rebecca blossomed under the rigorous Starfleet training and developed a keen interest in weaponry and tactical systems. She worked hard during her years as a cadet and graduated 6th in her class as a Weapon's Specialist.

Rebecca's first assignment was on Starbase 23. While stationed on the Starbase she was accepted to study Tactical Analysis under the renowned military strategist Commander Reynard Holton. She soaked up as much knowledge as possible under his tutorage and became well versed in tactical systems and strategies. Within a year her studies were rewarded and she was promoted to the rank of Lieutenant Junior Grade.

Wishing to put her new knowledge to work, she applied for a position aboard the USS Aries and was posted to the Security Department, where her knowledge and skills soon earned her the rank of full Lieutenant.

While serving aboard the Aries, Rebecca fell in love with an Engineering Officer named Benjamin Sinclair. At first they tried to play down their mutual attraction, fearing that their love would interfere with their careers. But, after several months, they decided that nothing could keep them apart and were married on Nimbus III in a small ceremony witnessed by several of their crewmates.

After almost two years of marriage, Rebecca was offered the position as Assistant Security Chief aboard the USS Bradbury. After an exhaustive debate, Rebecca and Benjamin finally agreed that she should accept the position in the hopes that Benjamin could transfer to the Bradbury soon.

One fateful day in 2372, Rebecca was on the bridge as the on duty tactical officer when the Bradbury came under attack by an alien race known as the Auroon. The bridge was heavily damaged and two of the bridge crew perished. However, Rebecca was able to stay at her post and was instrumental in helping to fend off the attack. Captain Stevenson recommended her for Starfleet Commendation and soon after Rebecca was promoted to the rank of Lieutenant Commander.

In 2375 Rebecca was offered the position of Security Chief aboard the USS Crazy Horse. She transferred to the new ship and was delighted when, soon after, her husband Benjamin was also transferred to the Crazy Horse. Their reunion was not all that she had hoped for though. After three years of separation, Benjamin seemed very distant and their relationship was strained. Rebecca and Benjamin opted to live in separate quarters and hoped to work out the difficulties in their relationship.

Rebecca and Benjamin both received promotions in 2376. Rebecca became a full Commander and Benjamin was promoted to the rank of Lieutenant Commander. Their relationship, although friendly, was still not what Rebecca had hoped for. They went into counseling and during their sessions together Benjamin revealed that he had a secret past he had been keeping from Rebecca and was still afraid to reveal. Try as she might, Rebecca could not unlock the secret that Benjamin held. Their relationship continued to deteriorate and in 2378 when Rebecca became aware that the position of first officer on the newly commissioned USS Endeavour under the command of Captain Marcus Forrester was open, she applied for it immediately.

Commander Sinclair's impeccable service record and knowledge of tactical systems and strategies were just the qualities that Captain Forrester had been looking for in a first officer. Her low voice and statuesque grace added regality to her command presence and he knew that she was well respected by the personnel under her command and adept at her dealings with any personal conflicts that might come up aboard ship. Having worked together on previous assignments, Forrester also knew that they would have a good working relationship on board the Endeavour. Sinclair's request for assignment was approved immediately and she began to look forward to the adventures that awaited her as first officer of the Endeavour with great anticipation.

Commander Sinclair is now the First Officer serving aboard the USS Alliance, under command of Captain Marcus Forrester.