[This post will be a work-in-progress, and will change as I become aware of new resources.]
A good place to start when
researching a wrestler, promotion, or other related subject are
newspaper archives. Every day hundreds, if not thousands, of pages of
old newspapers are being digitized, made searchable through OCR (optical
character recognition) technology and released to the web. Some such
resources are free to the public, some are provided as commercial
products. Some of those commercial options are available through
agreements with local public library systems, and so are effectively
free for patrons. For most of the following, I will just be using the
term 'wrestler' to include anyone associated with the business be they
actual wrestlers, referees, managers or promoters, just to save time.
Aside from just articles, ads and results for wrestling shows, newspapers also bring us news of accidents, deaths and obituaries, weddings, and often retrospective articles when a retired wrestler becomes something of a local icon.
Newspapers (free)
ChroniclingAmerica.log.gov is a newspaper digitization program headed by the United States Library of Congress, and has a goal to digitize all available newspapers that are in the public domain. That means the content is largely pre-1926. Through a partnership with Newspapers.com, a lot of the papers on Chronicling America are also available through the paid service, which boosts Newspapers.com's catalog but also allows for a much smoother user interface than what the LOC currently offers. This program is mostly executed by various state archives and university libraries, where they can receive government grants to digitize their newspaper collections and provide them to the Library of Congress to host on the Chronicling America site.
The Google Newspaper Archive (news.google.com/newspapers) is one of a long line of semi-abandoned Google experiments. Back when they were binge-scanning every book they could get their hands on, they also began digitizing newspapers, new and old. They also briefly bought out a website called PaperofRecord.com that happened to have the largest collection of Mexican newspapers on the web. Sadly, since Google was not able to work out an agreement with the Hemeroteca Nacional Digital de Mexico that had provided the Mexican papers, all of that content was removed from Google's site and, even once PaperofRecord.com was sold to another party, the Mexican papers were never restored and now remain mostly inaccessible outside of Mexico.
Mexican papers aside, the Google Newspaper Archive is still online and while the search facility is mostly useless the papers are still there and can be browsed directly. While many titles have now been removed, this collection still includes many titles that are available nowhere else, as yet. So it still a valuable, though tedious, resource for historical newspaper research.
Back to Mexico, there are a few newspapers that are free to search and read on the site for the Hemeroteca Nacional Digital de Mexico (http://www.hndm.unam.mx/), namely El Informador, the main newspaper of Guadalajara.
Aside from just articles, ads and results for wrestling shows, newspapers also bring us news of accidents, deaths and obituaries, weddings, and often retrospective articles when a retired wrestler becomes something of a local icon.
Newspapers (free)
ChroniclingAmerica.log.gov is a newspaper digitization program headed by the United States Library of Congress, and has a goal to digitize all available newspapers that are in the public domain. That means the content is largely pre-1926. Through a partnership with Newspapers.com, a lot of the papers on Chronicling America are also available through the paid service, which boosts Newspapers.com's catalog but also allows for a much smoother user interface than what the LOC currently offers. This program is mostly executed by various state archives and university libraries, where they can receive government grants to digitize their newspaper collections and provide them to the Library of Congress to host on the Chronicling America site.
The Google Newspaper Archive (news.google.com/newspapers) is one of a long line of semi-abandoned Google experiments. Back when they were binge-scanning every book they could get their hands on, they also began digitizing newspapers, new and old. They also briefly bought out a website called PaperofRecord.com that happened to have the largest collection of Mexican newspapers on the web. Sadly, since Google was not able to work out an agreement with the Hemeroteca Nacional Digital de Mexico that had provided the Mexican papers, all of that content was removed from Google's site and, even once PaperofRecord.com was sold to another party, the Mexican papers were never restored and now remain mostly inaccessible outside of Mexico.
Mexican papers aside, the Google Newspaper Archive is still online and while the search facility is mostly useless the papers are still there and can be browsed directly. While many titles have now been removed, this collection still includes many titles that are available nowhere else, as yet. So it still a valuable, though tedious, resource for historical newspaper research.
Back to Mexico, there are a few newspapers that are free to search and read on the site for the Hemeroteca Nacional Digital de Mexico (http://www.hndm.unam.mx/), namely El Informador, the main newspaper of Guadalajara.
Elephind.com is a sort of meta search engine that attempts to provide a single search interface for several of the various independent newspaper digitization sites across the world.
Newspapers (subscription)
Newspapers.com is a now subsidiary of Ancestry.com and is available through paid subscription. They probably have the largest catalog with the best user interface of the available commercial options, and are constantly adding new titles and pages to their offerings.
GenealogyBank.com is a subsidiary of Newsbank.com, and as the title implies, is geared more directly toward genealogical research, but still have an impressive catalog of newspapers in their archive. For the most part, there is not a lot of overlap with the titles offered at Newspapers.com, so a subscription to both, for those who could afford it, would be very useful.
NewspaperArchive.com has probably the smallest collection of the paid sites, and due to poor management, squandered their early lead in the field. They also racked up a lot of bad user sentiment with questionable billing practices and poor site performance. While those days are largely past, the company as it stands now is having to recover a log of lost ground. They are still adding new content, but they dont' really offer any convenient way to know what that is. For what they offer, they are also the most expensive of the three sites, but still, the do offer papers not covered by either Newspapers.com or GenealogyBank.com
Genealogy Resources
While genealogy sites might not immediately seem relevant to wrestling research, remember that family history research is largely just searching for information on specific people. And wrestlers are certainly specific people! Sites along these lines are perfect for fleshing out personal details about a wrestler's whereabouts at various points in their lives, before, during and after their wrestling careers. Sometimes tracking them down requires working from a different angle, such as finding a sibling or child and working back toward your main subject. Often you can reconstruct a part of their family tree and find living family members to talk to, who sometimes are only too happy to talk about their long departed loved ones.
Free sites:
FamilySearch.org is the primary genealogy website maintained by the Church of Jesus Christ of Latter Day Saints. The Mormons' enthusiasm for family history is a benefit for everyone due to the sheer volume of information they are constantly making available. The site contains census records (see where the wrestlers were born, where they lived, family members, etc.), immigration records (mostly ships passenger lists), city directories (sort of the precursor to phone books), vital records (birth, marriage, divorce and death records) and a variety of other records both civilian and military.
FindAGrave.com is another good resource, not just to locate the final resting place of a wrestler, but also possibly connections to family. Especially in the case of wrestlers long deceased, often it is through family that we might be able to find more about a wrestler.
Fold3.com is primarily an archive of military records, though they do also have some census records, immigration records and city directories. I have had a lot of success finding wrestlers from the 1910s-1950s in the World War I and World War II draft registrations. Those draft records typically include a full name, date and place of birth, and current residence. The WWII records also include employment information, height, weight, hair color, skin color, other distinguishing features (cauliflower ears!) and a copy of the wrestlers' signature.