Grievous was a well-known and respected strategist when, erm, alive. Palpatine approached him through Dooku to work for them. He refused. Strangely enough, his shuttle was blown up shortly after. Strangely enough, he was retrieved by a ship that just happened to be there with excellent medical facilities. Strangely enough, after his brain and bits were droided up, he became much more interested in helping out the to be-Emperor.
Look on the bright side; I can still out-geek you. 