Tobias Muldoon is an inventor in the latter part of the 19th Century. He is alternately a Decepticon patsy and a (slightly hapless) action hero.
IDW Hearts of Steel continuity
Muldoon invents a "sub-marine", the S.S. Vicuna, and attempts to demonstrate it for Mark Twain and Jules Verne in San Francisco Bay. It sinks. His primary investor, Stanford Merriweather, is not amused, and Muldoon's financial prospects (not to mention his chances of marrying Merriweather's daughter, Kitty) look bleak. He is then confronted by Shockwave, who offers to assist him in transforming the Earth.
Muldoon readily agrees to work with the Decepticons, providing them with plans for 19th-century bodies, and information on human society. When he realizes they are evil, however, he flees, and goes to Merriweather's house looking for help.
Muldoon is unsuccessful in convincing Merriweather, Kitty, or Twain (Merriweather's houseguest), until Ravage bursts in. He has been hunting Muldoon. Muldoon fends him off with a decorative sword and shield while the others escape, and (after Ravage is dispatched by Twain) receives Merriweather's full support in fighting the Decepticons.
Muldoon and the other protagonists pursue the Decepticons' Astrotrain, and Muldoon's heroic efforts to protect Kitty earn him Merriweather's blessing of their romance. Muldoon is trapped in a train tunnel by Decepticon explosives, but is soon freed by John Henry.