The Google Doodles is actually Google’s Logo which keep changing. You must have noticed that Google logo keep changes like on festival or seasons.
The very first logo was designed in the year 1998

Now days Google started holds a competition so called Doodle4Google which is for students in grades K–12 to create their own Google.doodle. Winning doodles go onto the Doodle4Google website, where the public can vote for the winner, who wins a trip to the Googleplex and the hosting of the winning doodle for 24 hours on the Google website.