It turns out that it was Arya Stark, the young Stark member who trains as an assassin to avenge the deaths of her family members. The role, of course, ended up going to Maisie Williams, who received two Emmy nominations for her performance as Arya.
In 2017, at a South by Southwest panel, co-showrunner David Benioff discussed what the process of casting Arya entailed (via Mental Floss). Benioff began by explaining that they found casting both Arya and Sansa to be a challenge because the characters are so young at the start of the series but then their arcs prove to be very dark and intense. However, casting Arya proved to take even longer than expected.
Benioff explained, “I remember we probably looked at 300 girls in England and could not find the right Arya.” Then, in the midst of looking at audition tapes when they came across Williams. The showrunner continued, “There was just something about that little tiny thumbnail face that just seemed right. She looked about seven. Like she was 12, but going on seven. So we clicked on the audition video and waited about 40 minutes for it to download. When we saw that audition video she was just f***ing awesome.”
