You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Doctor_Who

Context:
Doctor Who first appeared on BBC TV at 17:16:20 GMT, eighty seconds after the scheduled programme time, 5:15 pm, on Saturday, 23 November 1963. It was to be a regular weekly programme, each episode 25 minutes of transmission length. Discussions and plans for the programme had been in progress for a year. The head of drama, Canadian Sydney Newman, was mainly responsible for developing the programme, with the first format document for the series being written by Newman along with the head of the script department (later head of serials) Donald Wilson and staff writer C. E. Webber. Writer Anthony Coburn, story editor David Whitaker and initial producer Verity Lambert also heavily contributed to the development of the series.[note 1] The programme was originally intended to appeal to a family audience, as an educational programme using time travel as a means to explore scientific ideas and famous moments in history. On 31 July 1963 Whitaker commissioned Terry Nation to write a story under the title The Mutants. As originally written, the Daleks and Thals were the victims of an alien neutron bomb attack but Nation later dropped the aliens and made the Daleks the aggressors. When the script was presented to Newman and Wilson it was immediately rejected as the programme was not permitted to contain any "bug-eyed monsters". The first serial had been completed and the BBC believed it was crucial that the next one be a success, but The Mutants was the only script ready to go, so the show had little choice but to use it. According to producer Verity Lambert; "We didn't have a lot of choice — we only had the Dalek serial to go ... We had a bit of a crisis of confidence because Donald [Wilson] was so adamant that we shouldn't make it. Had we had anything else ready we would have made that." Nation's script became the second Doctor Who serial – The Daleks (a.k.a. The Mutants). The serial introduced the eponymous aliens that would become the series' most popular monsters, and was responsible for the BBC's first merchandising boom.

Question:
What creatures were the most popular monsters in the series?

The Daleks (a.k.a. The Mutants)