You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Genghis_Khan

Context:
The succession of Genghis Khan was already a significant topic during the later years of his reign, as he reached old age. The long running paternity discussion about Genghis' oldest son Jochi was particularly contentious because of the seniority of Jochi among the brothers. According to traditional historical accounts, the issue over Jochi's paternity was voiced most strongly by Chagatai. In The Secret History of the Mongols, just before the invasion of the Khwarezmid Empire by Genghis Khan, Chagatai declared before his father and brothers that he would never accept Jochi as Genghis Khan's successor. In response to this tension, and possibly for other reasons, Ögedei was appointed as successor.

Question:
Which Mongol leader was most opposed to Jochi as Genghis Khan's successor?

Chagatai