who is the engineer ?

An engineer is a professional practitioner of engineering, concerned with applying scientific knowledge, mathematics and ingenuity to develop solutions for technical and practical problems. Engineers design materials, structures, machines and systems while considering the limitations imposed by practicality, safety and cost. The word engineer is derived from the Latin root ingenium, meaning "cleverness".
Engineers are grounded in applied sciences, and their work in research and development is distinct from the basic research focus of scientists. The work of engineers forms the link between scientific discoveries and their subsequent applications to human needs.               

Conference of Engineers at the Menai Straits Preparatory to Floating one of the Tubes of the Britannia Bridge, by John Seymour Lucas, 1868