Life force was once described by the Eleventh Doctor as "basically the 'soul' of a living being". (TV: The Doctor, the Widow and the Wardrobe)

Many creatures had the ability to drain another's life force like Fendahl, (PROSE: The Left-Handed Hummingbird) or the mutated Lazarus, which could leave the victim looking like a dried husk. (TV: The Lazarus Experiment)

The First Doctor's life-force was drained by Mondas during the Cybermen's attack on Earth in 1986. This drain on his vitality triggered the Doctor's regeneration into his second incarnation. (TV: The Tenth Planet)

Abaddon fed off the life-force of living creatures, completely draining it from them. Jack Harkness, being a fixed point in time, had an over abundance of life-force. When Abaddon attempted to steal Jack's, there was too much, and Abaddon was destroyed. (TV: End of Days)

After his botched resurrection by the Disciples of Saxon, the Master was able to manipulate his life force. At the cost of slowly burning it out, he was able to jump mind-boggling distances, nearly flying, and to manipulate electricity-like bolts which he could fire from the palms of his hands. (TV: The End of Time) After his stay on the saved Gallifrey during which the Time Lords cured his "little condition", the Master was restored to normal, no longer dying or suffering of a ravenous hunger, but stripped of his special abilities. (TV: The Doctor Falls)

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