Lieutenant Commander Sheila Thatcher was a female Human of English descent who served as chief medical officer on the USS Incursion.
Dr. Thatcher grew up in London and joined Starfleet at a young age, where she was quickly recognized as a skilled healer. She is regarded as one of Starfleet’s foremost authorities on alien pathogens and disorders. She has been responsible for the curing of no less then seven alien diseases.
In 2377, Dr. Thatcher was one of the few members of the Incursion's crew who was not infected with the Warden virus and subsequently did not mutiny against Captain Refelian. As such, she was part of the group of loyalists who beamed over to a Borg cube holding the Incursion in its tractor beam to set antimatter charges to free the starship. Whilst on the cube, the away team discovered a Borg serum which turned out to be a cure to the Warden virus. Using the serum, Dr. Thatcher was able to restore the Incursion's crew back to their usual selves (Away Team: Qo'nos Rescue and Borg Rescue).
A short time later, she joined an away team to Romulus. Her role was to take medical scans of Romulans in the area, to test for Warden infection. Whilst the rest of the team set antimatter charges around Warden nanite factories, unfortunately the Borg decided to finish the job. The team was subsequently beamed them to the Borg cube in orbit, in preparation for assimilation. Fortunately for the team, the Incursion's technical advisor Data was able to punch a comm link into the Borg cube and lead Dr. Thatcher to her fellow teammates. Whilst instructing the team on how to disrupt the power systems of the cube, allowing the team and the Incursion (once again in a Borg tractor beam) to escape (Away Team: Demolition on Romulus and Borg Hostages). (ST video game: Away Team)