A CUBLAS developer uses NVIDIA's CUDA Basic Linear Algebra Subprograms (CUBLAS) library to optimize GPU performance in computing. They leverage CUBLAS to perform complex mathematical operations, such as matrix multiplication or solution of linear equations, more efficiently. Their work involves writing and maintaining code, debugging, and performance tuning. They also ensure that applications are scalable and compatible with various CUDA-enabled GPUs. Furthermore, they collaborate with other developers and scientists to integrate CUBLAS functionality into larger software systems, contributing to advancements in fields like machine learning, scientific computing, and computer vision.