Theatre director Tiit Ojasoo and interdisciplinary artist Ene-Liis Semper are the founders in 2005 and since then the two artistic directors of Theatre NO99. The two have formed an indispensable duo that together with the actors of Theatre NO99 has received considerable aclaim for their work across Europe. Ojasoo and Semper work in various formats, from doing productions that are presented in offices and other non-stage situations, to work presented in television, to film, to big scale stage productions for thousands of spectators at a time. Their works often combine visually expressive staging with fearlessly addressing the most complex societal issues.

Ene-Liis Semper (1969) studied set design at the Estonian Acacemy of Arts, graduating in 1995 and has since worked extensively in the fields of contemporary theatre and opera. Beside performing arts she is also an internationally acclaimed video artist and has represented Estonia at the Venice Biennale and at Manifesta. Her interdisciplinary experience has been crucial for the development of Theatre NO99. At Theatre NO99 she is with Tiit Ojasoo the co-author of the majority the theatre's productions.

Ojasoo's and Semper's work at Theatre NO99 has been invited by international festivals such as Festival d’Avignon (France), Wiener Festwochen (Austria), Theaterformen (Germany), NET (New European Theatre) and Golden Mask (Russia) and has been performed at venues throughout Europe such as Théâtre de l'Odéon in Paris, HAU in Berlin and Thalia Theater in Hamburg.

In addition to Theatre NO99 Tiit Ojasoo's and Ene-Liis Semper's international career has over the years included also working at Münchner Kammerspiele and Thalia Theater Hamburg (Germany) where their latest work was Peter Handke's „The Hour When We Knew Nothing Of Each Other“ that premiered in April 2015. That production was invited to Wiener Festwochen (Austria) and Ruhrfestspiele (Germany, both on 2015) and most recentl opened the Holland Festival (Netherlands, 2016).

It has been noted by many that a very central trait of Semper’s and Ojasoo's work as a director is the high level of scenic energy of his actors and also that the actors work as a well tuned ensemble. One of the specific qualities of his work is also the ability to develop societal metaphors out of very personal experiences and emotions.