Beck (The Lady in the Lake)

Beck was a Proto-Time Lord clone of River Song

Beck was created on Demons Run by Madame Kovarian, along with six other clones. After the Eleventh Doctor raided Demons Run, Beck escaped on a ship with the other six clones. As part of his religious cult, Lake convinced Beck to die multiple times on Terminus Prime so he could covertly study regeneration and find out how long he was able to live. (AUDIO: The Lady in the Lake)

After Beck and the other six initial clones were lost following the Doctor's raid of Demons Run and River married the Doctor instead of killing him, Kovarian created at least four additional clones: Brooke, H-One, H-Two, and O. (AUDIO: The Furies)

Behind the scenes
Like all of their siblings, Beck's name is a reference to water, with their name coming from the word beck, which is used as the common term for a brook in northern areas.