In addition to Juri Lotman and Jakob von Uexküll, there have been several other scientists at the roots of Tartu school of semiotics.
See his homepage
He has worked in Tartu in the years (1883-1893) when he formulated the main principles of his theory. About him, see
Dulicenko Aleksander D. 1993. O rezijanoloskih obravnavah J. Baudouina de Courtenayja v derpetskem obdobju 1883--1893 [On J. Baudouin de Courtenay's resianological publications during his Tartu period (1883-1893)]. Slavisticna revija 41(1-4): 381-389. [Abstract]
Jakobson Roman, Stankiewicz E. 1998. Baudouin de Courtenay as perceived by American linguists. In Sketches of Slavic Scholars, Henrik Birnbaum (ed.).
Stankiewicz E. 1988. The place of J. Baudouin de Courtenay in the history of modern linguistics. Russian Linguistics 12: 133-145.
About him, see
Dulicenko Alexander D. 2000. Über die Prinzipien einer philosophischen Universalsprache von Jakob Linzbach. Zeitschrift für Semiotik 22(3/4). [Abstract]