The Gradius series first game was Gradius released on 29th May 1985.
1985
Gradius
29th May 1985
1987
31st December 1987
1988
Gradius II: Gofer no Yabō
26th December 1988
1990
Gradius III
21st December 1990
1991
13th August 1991
Gradius: The Interstellar Assault
9th September 1991
1997
Gradius Gaiden
28th August 1997
2001
Gradius Advance
9th November 2001
2004
Gradius V
22nd July 2004
2007
23rd April 2007
Gradius II: Gofer no Yabou
13th November 2007
2012
18th October 2012
2015
22nd April 2015
2017
2nd February 2017
2019
Arcade Archives VS. GRADIUS
15th August 2019