Brooke (The Lady in the Lake)

Brooke was a Proto-Time Lord, grown from River Song's DNA, and a companion of the Fifth Doctor.

Creation
Madame Kovarian harvested Melody Pond's embryonic DNA in order to grow more children like her. This resulted in the creation of the Proto-Time Lords, the first batch consisted of seven siblings: Lake, Rindle, Tarn, Wadi, Creek, Stream, and Beck. (AUDIO: The Lady in the Lake)

The second set of siblings included: Brooke, H-One, H-Two, and O. (AUDIO: My Dinner with Andrew, The Furies) Brooke and the other Proto-Time Lords had the ability to regenerate; however, the exact amount of regenerations they each had was random. (AUDIO: The Lady in the Lake)

Travels with the Doctor and River Song
She had been sent on a mission by Madame Kovarian to kill the Doctor and joined him as his travelling companion. (AUDIO: The Furies)

She shared numerous adventures with the Doctor prior to their arrival on Terminus Prime. (AUDIO: A Requiem for the Doctor)

When River Song summoned the Doctor to Terminus Prime after witnessing the death of what she thought was the last of her siblings, Brooke was present in the TARDIS, leaving River shocked as she didn't recognise her, assuming the Doctor would be travelling with someone else at the time. Brooke complimented River's name and assured her that they were going to "get along". (AUDIO: The Lady in the Lake)

The Doctor, River and Brooke visited several places together. (AUDIO: The Furies)

The Doctor took Brooke and River to Vienna in the 18th century where they discovered that Mozart had completed his final piece and decided to investigate this anomaly, while also uncovering a series of murders which involved people corroding from the inside out. She was jealous of River and tried multiple times to get rid of her, which only made River more suspicious of her. She spiked the Doctor's tea with Aqua Galacia in an attempt to kill the Doctor with all of her hate for him; however, River counter-acted the hate with her love for the Doctor and left the Aqua Galacia in his system neutralised. (AUDIO: A Requiem for the Doctor)

Killing the Doctor
They later arrived at the Bumptious Gastropod where Brooke was supposed to meet with Kovarian following her assassination of the Doctor. Brooke was left with amnesia after River used her hallucinogenic lipstick on her, while the Doctor was left without any memories of both her and River. Brooke later shot the Doctor using regeneration inhibitors leaving him dead without the ability to regenerate. In retaliation, River shot and killed Brooke triggering her regeneration into a new incarnation and revealing her status as a Proto-Time Lord and one of River's siblings. (AUDIO: My Dinner with Andrew)

After she had killed once, Brooke found it difficult to stop killing. Once she had returned to Kovarian's spaceship, she killed the entirety of the crew on the deck and subsequently blamed this on River Song. She later acknowledged the legend of the Furies, noting how she liked that they would never give up. When H-One became jealous of Brooke being in Kovarian's favour, they got into a fight which resulted in Brooke murdering H-One. She attempted to blame this on River also. Eventually Brooke decided to side with River and turn against Kovarian, she took River's vortex manipulator and travelled back to the Bumptious Slug where she convinced Andrew Edwardson to take the Doctor's place, deceiving him into being killed by her earlier incarnation in the Doctor's place. She remained on Kovarian's spaceship with H-Two in order to torture Kovarian and attempt to find a way past her neural block. (AUDIO: The Furies)

Behind the scenes

 * The actress who played Brooke's second incarnation, Nina Toussaint-White, also played an incarnation of Melody Pond known as Mels in Let's Kill Hitler.
 * Like all of her siblings, Brooke's name is a reference to water, with her name coming from the word brook, which is a small stream.