Luke Siss

Siss is a member of the Scouting Legion who participates in the 57th expedition.

He first appears as a member of the expedition mounted from the Karanese District into the Titan-infested lands outside Wall Rose. He works with Ness to take down a deviant Titan in a field where their 3DMG can't be used to full effect; Ness takes out the Titan's ankles, and Siss destroys the nape of its neck when it falls.

[Spoiler] However, the two then encounter the Female Type Titan, who kills them both with ease when they attempt the same strategy on her. [/Spoiler]

Note: Siss is the official English translation by Kodansha.