Mis-filed in the SCO section of the WW1 Service Records (WO 363):

William SAMS, possibly William Leonard ... or William Charles ... or Robert William?

Born Hertfordshire, father Joseph, brothers George Charles (address Ontario, Canada), Frederick & Leonard. Sister Daisy. Home address Hertingfordbury, Herts.
Enlisted June 1904 - made a false statement on his attestation (not stated what!)
Enlisted again in the Dragoons, November 1907 (declared age 21yr 10m) & served until 1919. Mentioned in dispatches 1916. Reg Nos: 1445 & 34322.
Married Doris Victoria, home address Bradford.

Now the puzzle - enlisted and served as William Leonard.
The only Hertford birth I can find is William Charles (Q1 1887).
The only marriage of a Doris Victoria to a Sams is 1919, in Bradford, but the groom is Robert W.

Hopefully, if he's yours, the uncertain pieces will fall into place!

Anc****y, SCO, pages 58520 to 58564