Second One was the title given to a male who was in line for First One on Ligon II.

Hagon held the title until Yareena chose him as her First One and had Lutan, the former First One, "demoted" to Second One for his conduct during the time of the USS Enterprise-D's visit in 2364. (TNG: "Code of Honor")

The title may refer to female First Ones who have chosen not to challenge supersedence as well.