Final answer:
The Progressive Party formed by Theodore Roosevelt to challenge Taft's Republican Party was known as the Bull Moose Party, a name that reflected Roosevelt's forceful personality and progressive ideals.
Step-by-step explanation:
The Progressive Party, formed by Theodore Roosevelt to challenge President William Howard Taft's Republican Party, was also known as the Bull Moose Party. This nickname originated from Roosevelt's own words, indicating his robust health and unwavering conviction, famously claiming he was "as strong as a bull moose" after surviving an assassination attempt. Roosevelt's attempt to form this third party came about due to his frustration with Taft's nomination by the Republican Party, leading to a split where Roosevelt and his sought to champion progressive reforms.