Refers to a person who designs something, such as a building, system, or product. Often used in professional contexts.
He is a famous architectural designer.
Who is the designer of this system?
Compound of 設計 (sekkei, 'design') and 者 (sha, 'person'). The kanji 設 means 'establish' or 'set up', and 計 means 'plan' or 'measure'. 者 is a common suffix for agents.