A Cisco IOS developer designs, codes, tests, and troubleshoots Cisco's Internetwork Operating System (IOS), a proprietary software used to power most Cisco switches and routers. They work on enhancing the software's functionality, security, and performance, while also ensuring its compatibility with various hardware and networks. Their responsibilities include debugging, resolving system errors, and developing patches or updates. They also collaborate with other software engineers and network administrators to optimize system efficiency and implement new features. They must stay updated on the latest networking technologies, protocols, and standards to maintain the relevance and competitiveness of Cisco IOS.