Dr. Chronos

Dr. Chronos, a.k.a. the Time Merchant, is a mysterious and powerful alien humanoid who has full control over time and lifespans. He carries a large scythe and operates from an interdimensional technological base equipped with enigmatic machinery. He's even capable of annihilating entire planets and civilizations when he believes they have "used all their time".

Biography
Chronos materialized on a planet by accident while Will Robinson of the Jupiter II crew was conducting a scientific experiment, attempting to trap certain cosmic particles. Angered, the Time Merchant abducted Will and brought him to his own base to work for him and compensate for his misconduct. Will's father, Prof. John Robinson, followed through the gate along with the Robot and Dr. Zachary Smith, hoping to rescue Will. When brought to Chronos' base, Smith took the opportunity to hijack the alien's machine and used it to return to an earlier point of his lifetime, in 1997: right before the launch of the Jupiter II to be precise.

Smith intended to rewrite history by refusing to board the ship, but since his extra weight was what caused the ship to travel off-course originally; without him it would instead be fated to continue its way towards Alpha Centauri and be destroyed by an uncharted asteroid.

Chronos lamented that he couldn't bring Smith back without damaging his equipment, but Prof. John Robinson offered to trade away five years of his own life if the Time Merchant agreed to send the Robot back to convince Smith to change his mind and preserve history.

Appearances

 * Lost in Space, s03e18, "The Time Merchant" (1968)