There are several templates which can solo everything in Doom, my favorites are:
Sampire (all 70's suit, demon slayer weapon, undead slayer weapon, max swing speed)
Bard/mage
120 in music/provoke/discord/magery/med/EI
Tamer:
Many possible templates, with 120 taming/lore/magery/meditation. Vet is not required, as the necromancy casting Dark Father will keep you far away from your pet a lot of the time. It is possible to keep your pet healed with vet, but it is very difficult.
ABC:
Archery/bushido/chivalry, with resist/anatomy/healing
The tactics and items you need for each of these templates are completely different from the other templates, and I won't go into that here and now.
Between all of those, if I wanted to make a character to solo Doom, I'd make the ABC.
But my 115 bushido/mace/parry/100 tactics/100 spirit speak/100 necromancy whammy did wonderfully there as well before I switched up his template to fight peerless.