Hitman
Bionic Poster

Here are the key ones. Rank them in the way you see fit and let us know why.
Slam record broken = Breaks Nadal's record, and now has 24 slams. No player, male or female in history has more slams than him. This includes breaking Serena's open era record of most slam also.
Triple career slam = One ups Nadal's double career slam, by being the first male player to win the triple career slam. And first to do it across three surfaces. In the process he becomes the oldest RG and USO champion in history.
409 weeks at number one = Breaks Graf's record for most weeks at number one male or female, then proceeds to be the first player in history to smash the 400 week barrier. He is now going to be one week shy of 100 weeks ahead of Federer and 200 weeks exactly ahead of Nadal.
8th year ending number one = No player, male or female has more year ending number ones than Djokovic. In the process, breaks his own record to become the oldest world number one in history.
YEC record broken - Breaks Federer's record for most titles won, by winning his 7th title he stands alone. In process, he breaks his own record of being the oldest winner of the event, and longest gap between first and last win of 15 years.
40 masters titles barrier broken = Becomes the first player in history to win 40 masters titles, this includes winning every masters at least twice. He is one win away at MC from winning them all three times each.
71 big titles = First player to break the 70 big titles barrier, which includes 24 slams, 40 masters and 7 YEC.
Most slam finals played - He has played more slams finals than any player, male or female in history. He also has played the most semis finals, and is one quarter final away from playing the most quarters also, tied with Fed.
There are other achievements, such as first player to win a HC slam ten times, increasing top 5 and top 10 wins, to many to count, but I listed what I feel were the truly big ones.