According to TV Line Jesse Rath is playing Querl Dox / Brainiac 5 in a recurring role for Supergirl, starting with episode 10 titled “Legion of Super-Heroes.” This news comes a day after Blake Pitson got cast as Brainiac on the SyFy television series Krypton, which is a separate continuity from Supergirl, but does connect to the DC Films Universe.
Laura Vandervoort played Indigo aka Brainiac 8 earlier in the series, which is another descendant of Brainiac, so there’s that possibility of deeper connections dramatically.
Half computer, half organic life and boasting a 12-level intellect, Brainiac 5 is a member of the Legion of Super-Heroes who travels to National City from the 31st Century to help Supergirl and the DEO battle Reign, the villain that L-Corp CEO Samantha Arias (played by Odette Annable) is on track to becoming.
Fans of the comics will note that Brainiac 5 is the future descendent of Brainiac, who became a member of the Legion of Super-Heroes to make up for his ancestors wrong doings. Brainiac 5 also has a relationship with Supergirl in the comics.
Brainiac 5 was created by Jerry Siegel (Writer) and Jim Mooney (Artist) and first appeared in Action Comics #276 (1961).
Source: TV Line