Lake (The Lady in the Lake)

Lake, also known as the Great Lake, was a Proto-Time Lord clone of River Song and the leader of a religious cult.

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)

Incarnations of Lake
Sometime after escaping Demons Run, Lake 1 was tending to fuel cells with Wadi when one of the cells blew up in his face, the resulting explosion causing him to regenerate.

Lake 2 witnessed Rindle regenerate, just like he himself had previously done and became obsessed with discovering the mechanics of the process.

After murdering Mr Quisling, Lake 2 regenerated, but focused on Quisling, so that his next body looked like him.

Lily was Lake's fourth and final incarnation. (AUDIO: The Lady in the Lake)

Behind the scenes
Like all of their siblings, Lake's name is a reference to water, with their name coming from the word lake, which is a large area of water surrounded by land. The name of their female incarnation Lily is a reference to the water lily, an aquatic plant.