Who discovered Kenya?

It depends what you mean by 'discovered' as always. The remains of homo sapien dating from the Pleistocene era have been found here, and of course there were always natives. Arab traders were dealing with this area about 100 AD.

The first Europeans to explore this area was the Portuguese in 1498.

Kenya however was created by German colonisers in 1885, but they then became British. The Republic of Kenya dates from 1964 when they become independent of the British Empire.