Iudex Gundyr is the very first boss that you will encounter while playing dark souls 3.
He is not all that hard except for the fact that like many bosses in dark souls 3, he can grab you and throw you across the map & if positioned near the edge of the map can throw you off.
Start off by attacking him straight away when removing the sword from his chest to score in a good 3-4 hits then circle strafe around him counter clock wise (to the right) and you will kill him real fast. Be careful though! At around 35% health left he will transform & become very deadly if you let him hit you, However during his transformation you can get more free hits on him so he should be a problem.
Below is a video guide for this fight: