B'Elanna Torres
B'Elanna Torres is the chief engineer on the starship USS Voyager. She is another half-human/half-Klingon hybrid. And once again, in direct contradiction to the laws of biology, she marries Tom Paris, and they are able to conceive a child.
She was suspended from Starfleet academy for disciplinary actions concerning her inability to control her temper. Later she joined the Maquis after Chakotay saved her life. It was during her time with the Maquis that she and the rest of Voyager's crew were transported to the Delta Quadrant.
(in)Competence
Like the rest of Voyager's crew, she shows a total lack of intelligence. As Chuck Sonnenburg points out, she needs a tricorder to identify manure[1].
She is responsible for the Dreadnaught missile that ended up in the Delta Quadrant, as well. Initially it was a Cardassian weapon, but she reprogrammed it to attack a Cardassian target, and it backfired as she tried to talk it out of striking an unintended target on the wrong side of the galaxy. The thing found a planet with similar characteristics to its intended target while ignoring all other sensor data (stars in the wrong positions, non-Federation/Cardassian ships in the vicinity, etc.) on the grounds that Torres had been captured and was lying to it[2].