The Syphon Filter main theme is the theme song of the Syphon Filter series. It plays in every single game of the series.
It was composed by Chuck Doud in the trilogy, while other composers were in charge in the next three games.
Syphon Filter, 2 and 3
The theme is heard in the title screen for the first three games.
Syphon Filter: The Omega Strain
Mark Snow was responsible for composing the TOS theme. In this particular case, the theme was expanded and sounded longer than its trilogy counterpart. It also featured many more instruments than it did in the past, including a full orchestra, strings, choir, percussion and other sections. This possibly reflected the game's changing nature as compared to the trilogy.
Syphon Filter: Dark Mirror
Dark Mirror's version of the Syphon Filter theme was composed by Johnathan Mayer. He remixed Snow's version from the previous game and added a choir arrangement. Dark Mirror's version was much more sobering, due to the generally dark tone of the game. The choir was significantly prominent as compared to The Omega Strain, and the theme cut out faster than it did in the fourth game.
Syphon Filter: Logan's Shadow
As with Dark Mirror, Logan's Shadow featured a more sobering melody, and the tune was composed by Azam Ali. Logan's Shadow marks the first time that vocals were introduced into the Syphon Filter theme. Ali also developed Secret's Lament, the game's ending song.