This was a one-season western starring Syrian-American actor Michael Ansara, 
who a few years earlier played Cochise in the TV version of "Broken Arrow".

In this series he played an Indian who became a deputy sheriff. 
Law of the Plainsman was a spinoff from two episodes of The Rifleman,
where Ansara guest starred in the same role: U.S. Marshal Sam Buckhart.

Sam saved a white Army man's life in an ambush, so when he later died the man willed Sam a large sum of money....which he used to get an 
education at private schools and Harvard University.

At the start of this series, the Marshal befriends a little girl played 
by Gina Gillespie -- the only other regular.

Gina eventually retired from acting in her teens in the mid 1960s, 
and became a lawyer, which she is to this day.

Michael Ansara is also still alive but he retired about 10 years ago.