Samuel J Leffler is a computer scientist

Computer science

Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...

, known for
his extensive work on BSD, from the 1980s to FreeBSD

FreeBSD

FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...

 in the
present day. Among other projects, he created FlexFAX

HylaFAX

HylaFAX is the leading fax server for Unix-like computer systems. It uses a client-server design and supports the sending and receiving of faxes as well as text pages, on any scale from low to very high volumes, if necessary making use of large numbers of modems...

,
libtiff

Libtiff

Libtiff is a library for reading and writing Tagged Image File Format files. The set also contains command line tools for processing TIFFs. It is distributed in source code and can be found as binary builds for all kinds of platforms...

, and the
FreeBSD Wireless
Device Drivers.

The Design and Implementation series of books are regarded as very
high quality works in computer science. They have been strongly
influential in the development of the BSD descendants and have
contributed to their cohesive and well-thought-out nature.