A hypervisor developer designs and maintains hypervisors, the software that creates and manages virtual machines (VMs). They ensure the hypervisor can efficiently allocate system resources like memory, processing power, and storage to each VM. They work on enhancing the performance, security, and isolation of VMs. They also troubleshoot and fix issues that arise in the hypervisor. Additionally, they may develop APIs for the hypervisor and ensure compatibility with different operating systems and hardware configurations. Their work is vital for cloud computing, virtualized data centers, and any environment where multiple VMs are used.