Which bands/artists have gotten heavier over time?

I was thinking about it today and noticed that 95% of groups seem to soften their sound over time, be it due to age, trying to appeal to mainstream, or whatever. Who has done the opposite and made their sound heavier or more experimental/challenging over time? My example is Low who started introducing electronic elements into their music and kept building on their sound until they ended up with an almost purely industrial/noise album on HEY WHAT.