Microsoft today updated Cortana for iPhone with a significant redesign that has been available to Android users since December. As noted by Paul Thurrott, version 2.0 of the app is more responsive with redesigned calling, texting, and reminders and more immersive full-page answers with quicker page transitions.
Cortana's mobile redesign launched on Android in December
Cortana is Microsoft's equivalent of Siri for Windows PCs and smartphones, Xbox, iOS, and Android. The personal assistant enables users to ask questions, check the weather, schedule calendar appointments, set reminders, track packages, look up sports scores, and many other tasks that Siri is capable of.
Cortana is free on the App Store [Direct Link] for iPhone.
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Here are some answers:
https://en.wikipedia.org/wiki/Halo_(series)
http://halo.wikia.com/wiki/Cortana