Like many grassroots movements, it's difficult to pinpoint the origin(s) of the Tea Party movement. By its definition, a grassroots movement is the collective manifestation of several independent groups reacting to a common grievance. Its nature is one that lacks organization or clearly defined boundaries.
The original tea party - the Boston Tea Party - was a revolt of the fledgling American colonists against their oppressive British overlords. They were protesting against taxation without representation - the fact that they were forced to pay what they considered exorbitant taxes to the Crown, without having any representation in the British Parliament. The current Tea Party movement is a response to a wide variety of grievances, but can basically be summed up as a frustration with federal government. People believe that the government is too big, is overreaching, is attempting to regulate or get its hands in things that it shouldn't be involved with, and additionally, people think their elected representatives aren't really interested in listening to their concerns regarding these issues. These frustrations transcend party lines, although admittedly, many "Tea Partiers" define themselves as Republican.
The exact origins of the Tea Party movement are not universaly agreed upon. Most people believe that the movement began in earnest in 2009. Groups of bloggers, as well as CNBC's Rick Santelli, called for peaceful Tax Day protests to the Obama administration's proposed high price-tag agenda. While its origins are debated, one thing everybody involved with the Tea Party can agree on is the Obama administration HAS TO REIN IN GOVERNMENT SPENDING.