Following allegations of being endorsed by Psi Corps in the Presidential elections (And the Sky Full of Stars), Clark was appointed as Vice President to Louis Santiago.  Tired of following Santiago's differing opinions, Clark engineered his assassination (Chrysalis).  He feigned illness to disembark from Earthforce One before it exploded in orbit of Io (Hunter, Prey) and was exposed for his schemes when Ivanova discovered a transmission between him and Morden (Voices of Authority).

Following this discovery he initiated martial law in all of Earth's provinces (Messages From Earth), issuing illegal orders to mobilize Nightwatch (In the Shadow of Z'ha'dum) to maintain order and arrest possible traitors (Point of No Return).  Some Earthforce officers, including General Hague who spearheaded an underground organization to expose him (All Alone in the Night), and Babylon 5 Captain Sheridan, opposed these policies and fought back (Severed Dreams).  Clark resorted to taking ISN off the air when it reported against him (Severed Dreams) but re-established it as his own propaganda machine (Ship of Tears) that he uses as a weapon of war to discredit Sheridan (The Illusion of Truth, The Face of the Enemy).

Robbed of his associations with the Shadows, in a panic he tries enforcing his law on any breakaway colonies (Proxima 3, Orion 7, Mars) against which Sheridan commences his all-out assault (No Surrender, No Retreat).  When Sheridan's forces finally reach Earth, he commits suicide, intending to take the whole planet with him (Endgame).

Played by Gary McGurk, who had a semi-regular role in the comedy series Home Improvement.