In Pokemon diamond how do you get Dialga?

Answer 1

start from Mt. Coronet and get your way up to the top.
step 1: defeat the 7th gym leader in snowpoint city.

step 2: get the galactic key in veilstone city from a galactic grunt that is standing in front of the HQ.

step 3: go through the middle door in the vielstone HQ and go through the electric door with the galactic key.

step 4: walk around the middle to bottom to go up some stairs to find a room with an electric door and behind it a person use the galactic key then the person will talk to you this person it Cyrus the team galactic leader.

step5: defeat Cyrus and he will walk to the right follow him and go through the green or yellow transporter i cant remember.

step6: you will get took to a different room and another person will battle you beat him and you will release 3 legendary Pokemon.

step7: go to orgbourg city and go through the cave and go up and see the lake. go through it with surf and keep going up till you get into a different room and go up so you go down steps and travel to the tip of mt. cornet you will find it one day you will have to battle a duo then battle another duo this duo is commander mars and Jupiter with your friend with blond hair.

step8:when you beat him diagla will be awaken by then so you will have to battle him and catch him but i didn't battle him i used the master ball that Cyrus gave you when you battled him in step 5.

good luck!!!
you capture it
just find stairs up at mt coronet till u reach the very top. then u will see a cave. come in. finish all the galactics and catch dialga
go through mt. coronet and you should find spear pillar

Answer 2

After defeating Veilstone Galactic HQ, go to Hearthome Mt.Coronet entrance. Climb all the way to the top (it's not very complicated or long). You will battle Mars and Jupiter with Rival Pearl then Galactic Boss Cyrus. After that, make sure you save (in case you defeat Dialga) then go and battle Dialga! He is level 47 so be prepared.