I traced the district further back, Leonard’s predecessor was rat Leon B. Field, who held the seat from 1957 (when it was district 1) till 1979 according to
https://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=10542187
Prior to that he was in the House. Wiki lists his Senate service as being from 1953-81, which must be wrong, Leonard was elected in 1978.
Leonard did not run for reelection in 1988, so the Dem took an open seat. Curiously, he had run for Congress way back in 1974 against GOP incumbent John N. “Happy” Camp, holding him to an unimpressive 58-42% victory. Camp would lose reelection that November to Dem Glenn English and the GOP wouldn’t get that CD back for 20 years. Leonard also ran during his time in the State Senate for Lt Governor in 1986, but lost to a member of the Kerr family in the general. No Republican would win that office from statehood until Mary Fallin in 1994.
A cursory glance for ex-State Sen. Don Williams says he was a school board member in Balko (Beaver County), OK, before his Senate win. I don’t know who his opponent was.
Minor correction: Sen. Leon Field first won the seat in 1950 (then the 1st), not 1956/7, and then resigned sometime in 1979.
Prior to Tim Leonard in the 1979 special, no Republican had won that State Senate district since Ross Rizley in 1930 and 1932. Rizley ran unsuccessfully for Governor in 1938, but won the Congressional seat (then the 8th) in 1940 and held it until 1948 when he ran unsuccessfully for the U.S. Senate against ex-Gov. Bob Kerr (the Senate seat had been held by a Republican who was elderly and didn’t run again, Edward Moore, an ex-Dem turned Willkie Republican & anti-New Dealer who used his wealth to buy the Senate seat out from under the Dem incumbent). Rizley was later rewarded by Eisenhower in 1956 with a federal court appointment, holding it until his death in 1969.
Ah, yes, one other thing. I used an online reference guide from the 2005 Oklahoma Almanac to trace back the state legislators. They have a complete list going back to statehood, and you might want to use it to check against Wikipedia.
https://web.archive.org/web/20080920211100/http://www.odl.state.ok.us/almanac/2005/14-histry.pdf
The Senate starts at p. 755 (type into the pdf file) and the House at p. 713.