Brooke 1

Brooke 1 was the first incarnation of Brooke, a Proto-Time Lord, grown from River Song's DNA, and a companion of the Fifth Doctor.

Biography
Brooke 1 had been sent on a mission by Madame Kovarian to kill the Doctor and joined him on his travels. (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, including Gadalax Prime. (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 Galatia 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 Galatia 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)

Behind the scenes

 * Joanna Horton physically resembles an adult version of actress Sydney Wade who played the first incarnation of Melody Pond known as "the little (blonde) girl" in The Impossible Astronaut and Day of the Moon