Terry Welch is the scientist credited with the “Welch” in the Lempel–Ziv–Welch, or LZW, compression algorithm. He published the practical algorithm in 1984 while working at the Sperry Research Center.
LZW builds on earlier work by Abraham Lempel and Jacob Ziv, whose LZ78 compression method introduced dictionary-based encoding. Welch refined that general approach into a fast algorithm suitable for computer hardware and file-storage systems. The combined name preserves the contributions of all three researchers.
LZW became especially well known because it was incorporated into the GIF image format. Instead of storing every pixel value independently, it replaces repeated sequences with compact dictionary codes. This makes it effective for images containing flat colors, repeating patterns, and simple graphics.
A frequent mistake is choosing Jacob Ziv or Abraham Lempel because their names appear first in the acronym. They developed the foundational Lempel–Ziv technique, but Welch is the person represented by the final letter and name.