Inclusion Criteria:
* Have documented initial diagnosis of multiple myeloma according to international myeloma working group (IMWG) diagnostic criteria
* Meet treatment regimen-specific requirements as follows: Treatment Regimen A (teclistamab \[tec\]-daratumumab \[dara\]-pomalidomide \[pom\]) only: Participant has relapsed or refractory multiple myeloma and has received 1 to 3 prior lines of therapy, including exposure to a proteasome inhibitor (PI) and lenalidomide; Treatment Regimen B (tec-dara-lenalidomide \[len\]-bortezomib \[bor\]) only: Participant has newly diagnosed or relapsed/refractory multiple myeloma and is naive to treatment with lenalidomide; Treatment Regimen C (tec-nirogacestat \[niro\]) only: Participant has relapsed or refractory multiple myeloma and has 1) received 3 or more prior lines of therapy or 2) is double refractory to a PI and an immunomodulatory drug (IMiD) and triple exposed to a PI, an IMiD, and an anti-cluster of differentiation (CD)38 monoclonal antibody (mAb); Treatment Regimen D (tec-len) only: Participant has multiple myeloma and has received greater than or equal to (\>=) 2 prior lines of therapy, including exposure to a PI, an IMiD, and an anti-CD38 mAb; Treatment Regimen E (tec-dara-len) only: Participant has newly diagnosed multiple myeloma or if previously treated has received 1 to 3 prior lines of therapy, including exposure to a PI and an IMiD; Treatment Regimen F (tec-dara-len-bor) only: Participant has newly diagnosed multiple myeloma
* Have measurable disease at screening as defined by at least one of the following: serum M-protein level \>= 1.0 gram/deciliter (g/dL); or urine M-protein level \>= 200 milligrams (mg)/24 hours; or light chain multiple myeloma: serum immunoglobulin (Ig) free light chain (FLC) \>= 10 milligram/deciliter (mg/dL) and abnormal serum Ig kappa lambda FLC ratio
* A woman of childbearing potential must have a negative serum (beta human chorionic gonadotropin \[hCG\]) pregnancy test at screening and a negative urine or serum pregnancy test within 24 hours before the start of study treatment administration and must agree to further serum or urine pregnancy tests during the study
* A woman must agree not to donate eggs (ova, oocytes) for the purposes of assisted reproduction during the study and for at least 100 days after the last dose of study treatment
Exclusion Criteria:
* Prior treatment with any therapy that targets B-cell maturation antigen (BCMA): This exclusion does not apply to Treatment Regimen C
* Live, attenuated vaccine within 30 days before the first dose of study treatment
* Received a cumulative dose of corticosteroids equivalent to \>= 140 mg of prednisone within the 14-day period before the start of study treatment administration
* Active central nervous system (CNS) involvement or exhibition of clinical signs of meningeal involvement of multiple myeloma. If either is suspected, brain magnetic resonance imaging (MRI) and lumbar cytology are required
* Known to be seropositive for human immunodeficiency virus
