An iptables developer designs, creates, and maintains iptables, a user-space utility program that allows system administrators to configure the IP packet filter rules of the Linux kernel firewall. They work on the netfilter project, which is integral to Linux operating systems. Their responsibilities include writing code, debugging, and testing to ensure the functionality and efficiency of the firewall. They also work on features like packet filtering, Network Address Translation (NAT) and packet mangling. Additionally, they collaborate with other developers, system administrators, and network engineers to troubleshoot any issues and enhance the security and efficiency of the network.