If you're talking about the eight planets in our solar system:

* First: Mercury

* Last: Neptune

However, Pluto was reclassified as a dwarf planet in 2006. So, if you include Pluto in the list, then:

* First: Mercury

* Last: Pluto

It's important to note that there are many other dwarf planets and even more celestial objects beyond the eight planets, so the "last" planet really depends on your definition.