Apache Spark started as a research project at the UC Berkeley AMPLab in 2009, and was open sourced in early 2010. Many of the ideas behind the system were presented in various research papers over the years.
After being released, Spark grew into a broad developer community, and moved to the Apache Software Foundation in 2013. Today, the project is developed collaboratively by a community of hundreds of developers from hundreds of organizations.
You can get involved in Apache Spark development by reading how to contribute.