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 Parris 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 was transported to the Delta quadrant.
(in)Competance
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 also responsible for the Dreadnaught missle that ended up in the Delta quadrant as well. Initially it was a Cardassian weapon but she reprogrammed the it to hit 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 viscinity, etc) on the grounds that Torres had been captured and was lying to it.