Leslie Arzt was a high school teacher, and was one of the Oceanic 815 crash survivors on the mysterious island. He is played by Daniel Roebuck, and appeared in nine episodes and two mobisodes.
Little is known about Leslie Arzt, other than the fact that he was married at least three times. He has a doctorate in an unspecified scientific field, and he taught a ninth-grade science class. Arzt traveled to Sydney after talking with an Australian woman over the Internet for a year. Unfortunately, Arzt used his friend's picture as his own and the woman was less than impressed with the real appearance of Arzt. She slipped out of an expensive restaurant Arzt took her to and he never saw her again. Instead of staying in Sydney for as long as he originally planned, Arzt decided to catch an early flight back to the United States — Oceanic Flight 815.
Marooned on the island along with everyone else, Leslie Arzt began to see (at least in his mind) the survivors forming into cliques, much like those he saw while teaching science in high school. He believed Kate Austen got the better pieces of the wreckage for her shelter and that Jin caught fish only for a select number of people rather than everyone. While those select few spent their time together venturing around the island, Arzt spent his time collecting and cataloging insects he came across. He believed he discovered twenty new species in just a few weeks on the island. Aside from those new species, Arzt also found an example of the Medusa spider and shared that knowledge with Nikki Fernandez, which she would later put to fatal use. He tried to convince several of his fellow survivors to not move to the caves that Jack Shepard discovered, but the sound of the monster nearby scared him into changing his mind.
After nearly a month on the island it started raining regularly every afternoon, Arzt realized that it was the cusp of monsoon season. He insisted Michael must launch his raft before the trade winds shifted and started blowing south instead of north, which would ruin the raft's chances of traveling into a shipping lane. Once the raft was almost completed, Michael approached Arzt for some more weather information but Arzt revealed he made everything about the monsoon season up. He apologized and Michael shrugged it off. Arzt learned from Hurley that there was a hatch in the jungle and that Jack was going to get some dynamite to blow it open. He volunteered for the expedition because he knew the effect tropical heat had on dynamite. At the edge of the Dark Territory, he lost his nerve when Danielle Rousseau mentioned that Montand lost his arm there, but then ran into the monster and came racing back to join the group. At the Black Rock he warned that dynamite left in tropical heat sweats nitroglycerin, the most dangerous and unstable explosive known to man. He proved his point eloquently by blowing up in front of everyone.
- 1x22 - Born to Run
- 1x23 - Exodus (1)
- 1x24 - Exodus (2)
- 1x25 - Exodus (3)
- 3x14 - Exposé
- 6x01 - LA X (1)
- 6x02 - LA X (2)
- 6x03 - What Kate Does
- 6x07 - Dr. Linus
- 1x22 - Born to Run: Arzt warns the survivors that if the raft doesn't get launched soon, the winds will shift, blowing the raft towards Antarctica.
- 1x23 - Exodus (1): Arzt volunteers to go on the expedition to the Black Rock to help move the dynamite safely.
- 1x24 - Exodus (2): Arzt lectures the Black Rock expedition on how dangerous dynamite can be, while forgetting that it's a bad idea to gesture emphatically while holding some.
- 1x24 - Exodus (2): Explodes into tiny pieces after lecturing everyone about how dangerous the dynamite was.
- Fooled You: In interviews near the end of season one, the creators of the show said that Dr. Arzt would be a more prominent character in season two. That was a red herring to make his death a surprise.
- Language Puns: "Arzt" means "doctor (M.D.)" in German.
- 1x23 - Exodus (1): "Hey, nice speech. Plan's a little flawed, but nobody's perfect. [...] Yeah, your plan. You're gonna go in the jungle, and get some dynamite, and blow open a hatch, and then you're gonna hide everyone inside. You wanna keep a secret, don't tell the fat guy. [..] God knows how long that dynamite has been out there. And from what I can tell, Madame Nutso doesn't seem too concerned with how to handle it. So unless you want to blow up, I'm coming with you."
- 1x23 - Exodus (1): "Yeah, I wanted to help, and that was before Montand lost his frigging arm."
- 1x23 - Exodus (1): "That's Arzt, you idiot!"
- 1x24 - Exodus (2): "Now, nitroglycerin is extremely temperamental, so we're not going to take any more of this then we have to-" [explodes]