A short history of Google's algorithm updates
June 2009 - Google Caffeine
Google Caffeine was perhaps the largest update the search engine has ever performed. This involved a whole new way of indexing webpages, which resulted in a fresher index. Google searches were also doubled in speed. Google Caffeine also resulted in 'real time' events being given priority, and long tail searches became more important than single keywords.
April 2010 - Google Places
In April 2010, the Google Local Business Center was replaced by Google Places. This enabled small businesses to place themselves on the Google Map, and improve their page ranking. This update made it clear to local businesses that they needed to focus on local SEO, and optimise their websites with location based keywords.
February 2011 - Google Panda
In February 2011, Google began to penalise websites that contained poorly written, repetitive content. This put a lot of offshore content farms out of business as people realised their content needed to be written for their readers, and not purely for search engines. The Panda update forced webmasters to focus on quality, and has consistently been tweaked over the years.
April 2012 - Google Penguin
Keeping in line with the cute black and white animal theme, Google Penguin took the Panda update a step further. Google implemented this in a further attempt to rid its search engine of spam websites containing poorly written content. Penguin was better able to notice which sites had bought links, and which sites were using spun content.
August 2013 - Google Hummingbird
Google Hummingbird was released to make search queries more relevant. Google wanted to deliver search results that were wholly relevant to the query, as opposed to providing results based on an exact keyword match. This was thought to be the biggest update since Caffeine as it aimed to make the search engine more human. Again, Hummingbird prioritised content that read naturally, and was another step by Google to do away with websites that were full of overstuffed keywords and spun content.
April 2015 - Mobilegeddon
Dubbed Mobilegeddon by the media, the latest large update to be released focused on mobile search queries. With non-responsive websites not displaying correctly on mobile devices, Google removed these from their mobile search results to improve the mobile search experience. It is now vital for a website to either be responsive or have a separate mobile friendly site, otherwise it will only appear in the search engines if it is searched for by brand name.
Only time will tell what the future holds, but it's clear that every Google update is implemented with its users in mind.