Garry Gillard > gg > garry
There are some Germanic names starting Ga- or Gar- which have something to with being strong with a spear or whatever. A name like Gareth could be shortened to Gary.
There was a comic strip character called Garth1 who was a strongman: my mother once told me she thought of naming me that: I'm glad she didn't.
Garry with two RRs is a placename in Scotland: there is a Loch Garry on the River Garry. The Gaelic name is Garaidh/Garraidh. (There is also a Loch Garry in Glengarry in Ontario, named by some Scots who ended up there as a result of the so-called Highland Clearances.)
As far as I know, the first Gary to have that as his whole first name was Gary Cooper, whose original name was Frank. 'Cooper hired casting director Nan Collins to work as his agent. Knowing that other actors were using the name "Frank Cooper", Collins suggested he change his first name to "Gary" after her hometown of Gary, Indiana. Cooper immediately liked the name.' (Wikipedia) The city is named after a man whose last name was Gary.
The Barbadian cricketer Sir Garfield Sobers, was aka Gary. Another sportsman, Gary Lineker, born 1960, had the name from birth: he played roundball football.
Turning to the evil side, we remember Gary Gilmore 2, the last man in the USA to be 'executed' by firing squad, at his request, in 1977. And Gary Glitter, English glam rock singer and convicted child molester. His real name was Paul Gadd.
Wikipedia has a page for the given name Gary/Garry. The name reached its greatest popularity in the USA in 1954, the year after Gary Cooper was awarded an Oscar for High Noon.
1. There is a Shetland connexion with the comic-strip Garth: "In the backstory, Garth washed ashore in Shetland and was adopted by an elderly couple." (Wikipedia)
2. Gary Gilmore's life and execution were the subject of the The Executioner's Song (Norman Mailer, 1979) and the 1982 TV film with the same title, starring Tommy Lee Jones as Gilmore.