in his marriages and death certificate he is named Alexander Clark Glover with the father named James Glover who was a diamond cutter and his Mother's maiden name was Mary M'Lean or Mclean?
It's quite common for an illegitimate child to use his or her father's surname, but the father can only be named on the birth certificate if he accompanies the mother when she goes to register the birth, and signs the certificate at the same time as she does.
But in his Death certificate in brackets he is 'Formally Alexander Clark' and his mother is named Mary Clark instead of McLean.
Are you sure it's 'formally' rather than 'formerly'?
And in a 1891 census I've possibly found him on the HMS 'Mars' training ship docked at the river tay, it says he's from Buckie but I can't prove its him
The admission registers for the 'Mars' Training Ship are extant and, I believe, held by Dundee City Archives.
https://www.dundeecity.gov.uk/service-area/corporate-services/democratic-and-legal-services/archives/our-records Now I've just recently found a Birth Certificate of an Alexander Clark from Rathven in Buckie born illegitimate to a Helen Clark and her mother is marked with an X
Do you mean that instead of signing her name she just wrote 'X' and this signature was witnessed by someone else?
I need help proving that this Alexander Clark is my great grandfather and answer the question of why his mother has different surnames.
If his mother was born Clark and later married a Mr McLean, or vice versa, she would have had two surnames. In Scotland, women don't lose their maiden surnames on marriage, and they are indexed in the death records by both surnames (and if they are married more than once, they should be indexed by all their husbands' surnames).
Incidentally Rathven is not 'in' Buckie. It's the other way round. The town of Buckie is in the parish of Rathven, and the village of Rathven is next to, but distinct from, Buckie. Births in Buckie would be registered in the registration district of Rathven because the registration districts (except in the cities) were initially the same as the parishes.
Can you post extracts from his marriage and death certificates so that we can see exactly how his mother's name is recorded on both certificates?
BTW I see that in the 1901 census he was aged 22, and a railway shunter. If he was 22, and if his age is accurate, he would have been born between about April 1878 and March 1879. When he died in 1963, his age was recorded as 84. This also suggests a birth in either 1878 or 1879, depending on the date of death.
The staff records of some railway companies have survived and can help to piece together a story. I have never attempted this, but I know that there is a book about researching railway workers. See
http://www.sog.org.uk/books-courses/books-publications/my-ancestor-was-a-railway-worker