OK, so for the race I made him a variant human fighter with the fighting style being great weapon fighting and get the feat great weapon master but this build doesn't require human since you're a fighter and by 15th level you should've already taken 1 feat
The 3rd level is samurai and you get advantage on all attacks during the turn with fighting spirit
Skip to 15th level and you attack 3 times a turn but what you really want is the rapid strike which turns all advantage to an extra attack making your 3 attacks per attack action into 6 attacks...
Add action surge you have 6 more attacks
Get a mage to cast haste on you and you have 18 attacks per turn
Let's do the math and assume all the attacks hit cause why not
+10 for great weapon master
+5 for strength
You reroll 1s and 2s the likelihood of you rolling another 1 or 2 is lower but let's just use the average roll for fun which is 4 for each dice if you're using a great sword or maul
23×18=414 damage in the first turn
But that's if you hit every attack which is unlikely...
Unless you get the lucky feat
Welp this was by random character build thoughts if you want I can make a list for these since I have a lot of them
Goodnight my fjers