I was writing some crossword clues yesterday, and one of them was for the actor Ray Winstone. I looked him up on the internet for inspiration and saw that Wikipedia described him as often playing 'geezer' roles in films. I assume that geezer in this context means 'cocky wide boy'.
The OED definition of geezer is "A term of derision applied especially to men, usually but not necessarily elderly". The geezer entry has not been edited for a long time, and I think that this definition is outdated. I don't think geezer is always used in a derisive way - it is used more as a slang word for 'man', perhaps - often with a connotation of a crafty or cunning quality. It often comes up in the combinations "old geezer", "some geezer", "some old geezer" or "there was this geezer". There is also the term diamond geezer, which means 'good bloke'. The music hall singer Albert Chevalier had a song, Knocked 'Em in the Old Kent Road, which began "Last week down our alley came a toff, Nice old geezer with a nasty cough", so geezer is not used negatively there.
The OED says that geezer is a dialect pronunciation of guiser, a masquerader or mummer. Eric Partridge in The Dictionary of Historical Slang considers the suggestion that Wellington's soldiers may have picked up the Basque word giza, meaning man or fellow, in around 1811, and changed this to geezer. Partridge also says that in the 1890s a geezer was more likely to be a woman.