These rules replace the rules for the leadership feat found on page 106 of the DMG.
1.) You must be sixth level.
2.) You must take the Leadership feat, and also designate a feat as back up. This back up feat will be used should your cohort not be present. Additionally, if your backup feat involves the crafting of items (such as Craft: Wand, etc.) then the amount of time units spent to utilize this feat is doubled.
3.) You cannot create your own cohort but you can choose any NPC in the campaign who would qualify (see below) as one. In other words, the DM creates the cohort, not you.
4.) A DM who creates an NPC may not later choose that same NPC as a cohort for one of his characters.
5.) In order to qualify as a cohort, he or she must be at least one level less than you at all times. If your cohort ever surpasses you in level (or reaches your level, say via your death) then they will cease to be your cohort. If your level surpasses the NPCs again you can regain them as a cohort.
6.) The DM controls the cohort’s advancement and gear acquisition. While you might want him or her to take another level of, say, “Barbarian”, the DM might decide that he or she really wants to learn more about The Planes (i.e. take a level in Expert). In other words, if you really want him or her to take that Barbarian level then you need to convince him or her in character to stop studying so much.
7.) The DM role-plays the cohort but in combat the player will control him or her. The DM has veto-power, however, on any action he feels is inconsistent with the character’s personality (e.g. “I’m going to have Cohort charge these evil fey!”. DM: “No, he won’t do that, he loves all fey, even the evil ones.”). In other words, the DM controls the cohort’s personality/psyche. A cohort is NOT another character for the PC to control.
8.) Once an NPC is selected as a cohort he/she will become one level less than the PC to which they belong if necessary. Note: NPCs of equal or greater level cannot be selected as cohorts.
9.) Once an NPC is selected as a cohort he/she will be given wealth according to Table 4-23: NPC Gear Value found on page 127 of the DMG if necessary (in other words, the minimum wealth for the newly made cohort shall be in accordance with Table 4-23). After that they will receive two shares of the treasure haul for any adventure they go on while the PC’s receive three shares.
10.) The benefit of having a cohort is that you get to have someone who is loyal to you within the group, a person you have much influence over. But they become mere magic items if you allow the player to control them completely. They’re still individuals who have their own wants and needs.
11.) Cohorts have access to anything the same way PCs do, via either core-book material or the things that have been unlocked using UPs. In addition, cohorts have access to anything on their personal list of unlocked items.
12.) At any time a player may decide to “fire” his cohort and “hire” a new one. This should be something that makes sense in character and is subject to DM approval.
13.) Players who desire a particular kind of cohort, but have yet to see an NPC that suits their tastes introduced in the campaign, are encouraged to discuss this with a DM. While rule 3 still applies, a DM can always be “inspired” to introduce an NPC that fits your preferences in the future.