Explanation:

- Option: 1, Ajit Pawar - Ajit Pawar is an influential politician in Maharashtra, often associated with the Nationalist Congress Party. However, he was not directly linked with the launch of the MTHL's first phase on 15th January 2020.

- Option: 2, Devendra Fadnavis - A key leader from the Bharatiya Janata Party, Devendra Fadnavis served as the Chief Minister of Maharashtra but did not launch the MTHL in January 2020.

- Option: 3, Narendra Modi - As the Prime Minister of India, Narendra Modi has inaugurated numerous infrastructure projects. Still, the MTHL phase one in January 2020 was not among them.

- Option: 4, Uddhav Thackeray - Uddhav Thackeray, serving as the Chief Minister of Maharashtra in 2020, was the leader who launched the first phase of the Mumbai Trans Harbour Link on 15th January 2020.