Helios is a fully trustless, efficient, and portable Ethereum light client written in Rust. Helios converts an untrusted centralized RPC endpoint into a safe unmanipulable local RPC for its users. It syncs in seconds, requires no storage, and is lightweight enough to run on mobile devices. The entire size of Helios's binary is 13Mb and should be easy to compile into WebAssembly. This makes it a perfect target to embed directly inside wallets and dapps.