The most common and most likely answer to this crossword clue is the 5 letter word DALEK
I've seen this crossword clue in The Times
D
A
L
E
K
More clues leading to the result DALEK
- Youth from east extremely knowledgeable about robot
- Exterminator in valley beginning to kill
- It exterminates product of yeast that’s in decay, reportedly
- Alien creation, valley with king
- Who’s enemy of the king beyond the valley?
- Who has this enemy?
- Famous doctor up against first of killers – this?
- Shake ladder: when centre pivots, he can’t climb it
- Hostile alien in valley, leader of Klingons
- Valley bleak at its nadir, soulless thing
Buddy explains!

The straight part
We know that "robot" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case robot = dalek.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DALEK mean?
DALEK noun- A member of a species of extraterrestrial cyborg mutants who appear in the television programme Doctor Who and are known for travelling in metallic shells, having monotone, mechanically distorted voices, repeating a limited number of phrases, and being bent on exterminating other beings mercilessly.
- One who is dogmatic, unfeeling and determined.