 In Russian Orthodox mysticism, "Sophia" became increasingly indistinguishable from the person of the Theotokos (rather than Christ), to the point of the implication of the Theotokos as a "fourth person of the Trinity".Such interpretations became popular in the late 19th to early 20th century, forwarded by authors such as Vladimir Solovyov, Pavel Florensky, Nikolai Berdyaev, and Sergei Bulgakov.Bulgakov's theology, known as "Sophianism", presented Divine Wisdom as co-existent with the Trinity, operating as the feminine aspect of God in concert with the three masculine principles of the Father, the Son, and the Holy Spirit.