Answer: Daleks

In the Sci-Fi universe of the iconic show Doctor Who there are more than a few bad guys of various shapes, sizes, and intergalactic origin. Of all the enemies the Doctor has encountered over the years, however, none has proven to be more enduring in the plot of the show or the hearts of the fans than the Daleks.

Daleks are a race of cyborgs, a hybrid of electro-mechanical suits and the bodies of aliens known as Kaleds, from the planet Skaro. Much like The Borg from Star Trek, Daleks are cybernetically enhanced, hive-minded, completely without compassion or remorse, and totally focused on taking over the entire universe so that none but their kind remain.

Bonus trivia: The Daleks tank-like appearance is quite purposeful. Writers wanted to avoid the sci-fi cliche of robots being simply men in metal suits and opted instead to have the Daleks more closely resemble a sort of futuristic military vehicle than a bipedal robot.