Henry Cabot Lodge is generally seen as the leader of the people in the Senate who wanted to reject the Treaty of Versailles. In general, they wanted to reject the treaty because they did not like the idea of the League of Nations.
Many senators did not like the idea of the League of Nations. They felt that the League would be a danger to American sovereignty. They believed that it would force us to get involved in wars that were not really our business. This was because the members of the League promised to defend one another from attack. In other words, if one country was attacked, the other countries were supposed to defend that country. Lodge and others believed that this would force the US to get involved in wars even if it was not in our interest to do so.
Thus, we can say that Lodge was the leader of the senators who wanted to reject (and who actually did end up rejecting) the Treaty of Versailles.