Seeking the identity/origins of the William Lockyear who m. Ann Martin at Tavistock, 03 Mar 1815.
This William was living in Tavistock at the time of the 1841 Census, age suggests a birth 1784, born in Devonshire.
He is likely the "William Lockyear alias Schearling" who died in 1850 in Tavistock, his age at death suggests a birth year of 1784.
Have you thought about obtaining the 1850 death certificate to see who was the informant?
For what it's worth William and Ann had at least one child, Ann Martin Lockyear, who was baptized in a non-conformist ceremony 12 Dec 1831 at Tavistock. This daughter Ann was living with both parents in 1841 and then with her widowed mother Ann (Martin) Lockyear at the time of the 1851 Census.
For info
possible other baptisms
Thomas Martin Lockyer
Birth 12 Oct 1817
Baptism 16 Oct 1817 Tavistock, Devon
Denomination: Independent
Father: William Lockyer Mother: Ann
Elizabeth Lockyer
Birth 13 Jul 1819
Baptism 14 Jul 1819 Tavistock, Devon
Denomination: Independent
Father: William Lockyer Mother: Ann
William Lockyer
Birth 22 May 1822
Baptism 25 May 1822 Tavistock, Devon
Denomination: Independent
Father: William Lockyer Mother: Ann
Elizabeth Lockyer
Birth 13 Apr 1824
Baptism 17 Apr 1824 Tavistock, Devon
Denomination: Independent
Father: William Lockyer Mother: Ann
Edit to add
could this be a possibility for William Lockyear’s death ?
LECKYEAIR, WILLIAM age 66
GRO Reference: 1850 J Quarter in TAVISTOCK Volume 09 Page 321
FreeBMD
Deaths Jun 1850
LOCKYEAIR William Tavistock 9 321
LOCKYHAIR William Tavistock 9 321
ADDED - I’ve just noticed that the 1850 death you mention for William Schearling has the same reference numbers vol 9 page 321