Mine was the James Bond theme on an old acoustic that was so old it smelled old, called a 'Milner Cello Guitar' that my Grandad brought with him to London from Stirling (in the 1930s!). Played subtlety and with bronze file-ings with a Victorian Penny, aged about 10.
Got a cheapo electric and WEM amp and started playing Stranglers bass lines and stuff by The Jam. Then sussed Hey Joe and Wild thing, then seek and destroy, got a Charvel and wanted play anything and everything. Still do but, mostly try and make my own riffs up like most of us and promptly forget them!