Kyle is a Generation II Core introduced in Portal 5. He is part of the 'Core Solution Project', and is Core Solution Two. He is very eloquent and intelligent, but is also incredibly quick to anger. He is also cunning and imaginative. He attempted to take over the Aperture Science facility thrice, and succeeded the third time. However, the facility was eventually retaken by Chell Clone 2076, Mac, several personality cores, and their 'army'. The fate of Kyle is currently unknown, but theorized. It is said that his fate will be stated in the 'second generation' of the Portal games, AKA all games after the eleventh game(which I don't know if I'll ever get to, having only basic plots for 7-9).
Interestingly, none of the other cores know or remember him at the time of his takeover. It is possible that he was in some sort of exclusion.